MCQs on Chemistry (General Science) for Govt. Exams

• Graphite is used in pencil because it is extremely brittle.
• By applying a small amount of pressure on graphite it breaks thus used as an extremely excellent tool for writing.
• Graphite and clay are used and the proportion of graphite to clay is adjusted according to the hardness required.

• Graphite is a non-metal that is conducting in nature and lubricating in nature.
• Graphite has slippery layers of carbon bound by weak covalent forces. it is extremely soft. Due to these reasons, it is used to make pencils.
• Graphite produces black marks which are used in drawing as well as writing.
• Uses of Graphite:
  • ​Writing Materials as in Pencil lead.
  • Lubricants in high temperature.
  • Nuclear Reactors as an absorber of neutrons.
  • In Batteries as electrodes.
  • Graphene Sheets i.e 100 times stronger and 10 times lighter than steel.

Mendeleev classified elements into seven periods and eight groups.

• During the period 1869 to 1872 A.D, the Russian scientist Dmitri Mendeleev developed the periodic table of elements.
• The vertical columns in Mendeleev’s periodic table are called groupswhile the horizontal rows are called periods.
• Mendeleev considered the fundamental property of elements, namely, the atomic mass, as standard and arranged 63 elements known at that time in increasing order of their atomic masses.
• Mendeleev’s periodic table is the most important step in the classification of elements.

Limitations of Mendeleev's periodic table:

• Elements with large differences in properties were included in the same group. For example, hard metals like copper and silver were included along with soft metals like sodium and potassium.
• No proper position could be given to the element hydrogen.

• Au(Gold) is the most ductile metal.
• Ductility is the property of being drawn into wire.
  • It is a permanent strain that accompanied fracture in a tension test.
  • It is a desirable property in machine components that are subjected to unanticipated overloads or impact loads.
  • The ductility of the metals decreases as the temperature increases because metals become weak at increasing temperatures.

• Aluminium is called green metal because it is a very environmentally friendly metal.
  • Recycling this material saves 95% of the energy required to produce aluminium from raw materials.
• It is called as green metal as it is environment friendly because of its properties like :
  • High durability
  • Lightweight
  • Malleability strength
  • Corrosion-free
  • Do not catch fire
  • It can be easily recycled

• Alpha particles are composite particles consisting of two protons and two neutrons tightly bound together.
• They are emitted from the nucleus of some radionuclides during a form of radioactive decay, called alpha-decay.
• Alpha particles were identified as helium-4 nuclei.
• These particles have the minimum penetration power and highest ionization power.
• They can cause serious damage if get into the body due to their high ionization power.
• A piece of paper or the outer layers of skin is sufficient to stop alpha particles.
• Radioactive material that emits alpha particles (alpha emitters) can be very harmful when inhaled, swallowed, or absorbed into the blood stream through wounds.

• Helium is a chemical element with the symbol He and atomic number 2.
• It is a colorless, odorless, tasteless, non-toxic, inert, and monatomic gas.
• It's the first in the noble gas group in the periodic table.
• It's boiling and melting point are the lowest among all the elements.
• The most familiar use of helium is as a safe, non-flammable gas to fill party and parade balloons.
• Helium is a critical component in many fields, including scientific research, medical technology, high-tech manufacturing, space exploration, and national defense.

Electronic configuration of halogen group is ns2 np5.

Halogens:

• The halogens are located on the left of the noble gases on the periodic table.
• They have seven valence electrons (one short of a stable octet).
• The halogen elements are fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts).
• Electronic configuration of halogen group is ns2 np5.

Electronic configuration :

• The arrangement of electrons in the electronic levels of an atom is called its electronic configuration.
• The electrons are arranged according to their energies and space availability.
• The electrons in the completely filled shells are known as core electrons.
• The electrons that are added to the electronic shell with the highest principal quantum number are called valence electrons.

There are a few sets of rules which we follow while arranging the electrons in an atom. They are-

• Aufbau principle-
  • ​It states that the atomic orbitals which have lower energies are filled first.
  • Then the electron goes to occupy the higher atomic energy levels.
  • This ruled is followed to write the electronic configuration of atoms in their ground state.
  • When in the excited state, the electrons might vacant the lower energy state and move on to a higher energy state.
  • The order in which atomic orbitals are filled are: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p.
  • The order follows that the lower ( n + l ) value of atomic orbital will have lower energy, where n = principal quantum number and l = azimuthal quantum number.
• Pauli's exclusion principle:
  • ​An electron is characterized by four quantum numbers n, m, l, and s.
  • Pauli's exclusion principle states that every electron must have its unique set of these four quantum numbers.
  • No two electrons can have the same set of quantum numbers.
  • Simplifying, we may say that an orbital can contain a maximum of two electrons and the two electrons should have opposite spins ( + ½, - ½ ).
• Hund's rule of maximum spin multiplicity:
  • ​While filling up the orbitals of the same energy, or degeneracy, electrons will first singly occupy the subshell.
  • After each subshell has been singly occupied, electron pairing will start.
  • This rule thus implies that maximum spin should be maintained while filling up electrons in a subshell.
  • The maximum spin state involves maximum exchange energy and yields a more stable state.
• Modern periodic law:
  • ​The modern period table involves the arrangement of the elements according to their increasing Atomic number.
  • The law states that the physical and chemical properties of an element are characteristics of its Atomic number.

• Magnesium is a chemical element with the symbol Mg and atomic number 12.
• It is a shiny gray solid that shares many physical and chemical properties with the other five alkaline earth metals
• Magnesium is a component of bone.
• It is also involved with the activity of bone-building cells and the parathyroid hormone, which regulates calcium levels
• Magnesium has two electrons in its outermost shell. Hence option 3 is correct.

• The electrons present in the outermost shell of an atom are known as the valence electrons.
• ​Valence also spelled valency in chemistry, is the property of an element that determines the number of other atoms with which an atom of the element can combine.
• Introduced in 1868, the term is used to express both the power of the combination of an element in general and the numerical value of the power of combination.
• The outermost shell of an atom can accommodate a maximum of 8 electrons.

• In a compound, the elements are chemically combined in a fixed proportion by mass.
• The Law of definite proportions states that a compound will always contain the same proportion of elements by mass.
• It was given by Proust.
• Lavoisier discovered the role of oxygen in combustion.
• Democritus was a Greek Mathematician.
• Dalton gave the atomic theory which states that the atom of different size varies in size and mass.

• It is an allotrope of carbon.
• It is a soft, greasy, dark greyish-colored crystalline solid.
• It is a good conductor of heat and electricity.
• It is chemically more reactive than diamond.
• Graphite is used in making electric furnaces and in making lead pencils.​
• In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array.

• Allotropes are different forms of the same element in the same physical state.
• Carbon has mainly 4 allotropes:
  • Diamond, Graphite, Fullerene, and Graphene.

If a hydrocarbon has any double bond, it is an alkene.

Hydrocarbons are the derivates of carbon and hydrogen compounds. In organic chemistry, Hydrocarbons are classified into three:-

1. Alkanes
2. Alkenes
3. Alkynes

1. Alkanes: These are represented by Single Bond between two carbons.

• The chemical formula CnH2n+2
• the first member of the alkane group - Methane (CH4)
• Symbolic representation of alkanes is —C—C—
• Methane is colourless, odourless, flammable gas. it is used primarily as fuel to make heat and light. it is used in the manufacturing of organic chemicals.

2. Alkenes: Theseare represented by a Double Bond between two carbons

• The chemical formula CnH2n
• The first member of the alkene group - Ethene (C2H4)
• Symbolic Representation of alkenes is —C=C—
• Ethene is used in the production of ethylene glycol ( 1,2-ethanediol ) an automotive anti-freezing agent, used in the production of polymers such as polyethene, polyvinyl chloride, and polystyrene.

3. Alkynes: These are represented by a Triple Bond between two carbons

• The chemical formula CnH2n-2
• The first member of the alkyne group - Ethyne (C2H2)
• The symbolic representation of alkynes is —C=C—
• Ethyne is also called Acetylene which is used in portable lighting, welding, and cutting, production of Chemicals.

• The extreme right side of the elements in the periodic table is classified as Gases as it consists of Noble Gases.
• Basically, the upper right side of the periodic table contains complete non-metallic elements.
• The halogen elements have zero metallic characters.

• Metallic elements are present at the extreme left side of the periodic table.
• Except for the hydrogen element which is present on the left side but is a non-metal.
• The middle elements in the periodic table are also metallic in characters.

Metalloids

• Metalloids are elements that can show both acidic and basic character.
• They are present between metals and non-metals.
• Arsenic, silicon, germanium, etc are examples of metalloids.

Gases

• Gaseous elements also come under non-metallic elements.
• But we cannot classify the elements of periodic as present on the right or left side as solids, liquids, and gases.
• Gas is a state of matter and not a class of elements.
• Hydrogen, oxygen, nitrogen, etc are the gaseous elements.

• The rarest stable element found in the crust of the Earth is osmium.
• Its atomic number is 76 and its symbol is Os.
• It belongs to the family of platinum transition metals and is glossy, blue-grey or blue-black.
• It is very hard and brittle and has a very high melting point (the fourth highest of all the elements).
• The densest naturally occurring element is osmium.
• It is frequently discovered in nature, either in its pure form or as an alloy, primarily in platinum ores.
• It is used to create extremely hard alloys for electrical contacts, instrument pivots, and fountain pen tips.
• It serves as a catalyst in the chemical sector as well. ​

• Palladium:
  • It is a chemical element with the atomic number 46 and the symbol Pd.
  • It is a rare, gleaming silvery-white metal.
• Iridium:
  • It is a chemical element with the atomic number 77 and the symbol Ir.
  • It is a platinum group transition metal that is extremely hard, brittle, and silvery-white in color.
  • It is regarded as the second-densest naturally occurring metal.
• Ruthenium:
  • It is a chemical element with the atomic number 44 and the symbol Ru.
  • It is a rare transition metal from the periodic table's platinum group.

• E. Rutherford (1871-1937) was born at Spring Grove on 30 August 1871.
• He was known as the ‘Father’ of nuclear physics.
• He is famous for his work on radioactivity and the discovery of the nucleus of an atom with the gold foil experiment.
• He got the Nobel prize in chemistry in 1908.

J.J. Thomson

• J.J. Thomson (1856- 1940) a British physicist was born in Cheetham Hill, a suburb of Manchester, on 18 December 1856.
• He was awarded the Nobel prize in Physics in 1906 for his work on the discovery of electrons.
• He directed the Cavendish Laboratory at Cambridge for 35 years and seven of his research assistants subsequently won Nobel prizes.

Neils Bohr

• Neils Bohr (1885-1962) was born in Copenhagen on 7 October 1885.
• He was appointed professor of physics at Copenhagen University in 1916.
• He got the Nobel prize for his work on the structure of the atom in 1922.

• The weight of iron increases when rust occurs.

• The main cause of corrosion is the presence of moisture, carbon dioxide, and oxygen in the air.
• When iron or any other metal oxidizes, oxygen from the air combines with the iron to make rust or iron oxide.
  • So, the weight of the bar increases due to the increased weight of oxygen, which has combined with the iron.
• Generally, it has been found that rusting occurs only when the iron is exposed to moisture while corrosion does not occur in dry air or vacuum.

• The vertical columns of Periodic Table is called Groups.
• In chemistry, a group is a column of elements in the periodic table of the chemical elements.
• There are 18 numbered groups in the periodic table; the f-block columns (between groups 2 and 3) are not numbered.
• The elements in a group have similar physical or chemical characteristics of the outermost electron shells of their atoms (i.e., the same core charge), because most chemical properties are dominated by the orbital location of the outermost electron.
• Groups may also be identified using their topmost element, or have a specific name.
• For example, group 16 is also described as the "oxygen group" and as the "chalcogens".
• An exception is the "iron group", which usually refers to "group 8", but in chemistry may also mean iron, cobalt, and nickel, or some other set of elements with similar chemical properties.
• In astrophysics and nuclear physics, it usually refers to iron, cobalt, nickel, chromium, and manganese.

• In chemistry and physics, a valence electron is an electron in the outer shell associated with an atom, and that can participate in the formation of a chemical bond if the outer shell is not closed.
• A period in the periodic table is a row of chemical elements. All elements in a row have the same number of electron shells.
• The s, p, d, f and g are called atomic orbitals. Filling up these orbitals with electrons builds atoms, and the way in which atoms are build up gives rise to the periodic table.

Allotrope: The different structure of same chemical compound is called Allotrope.

Graphite

• It is a soft greyish black crystalline substance.
• It was discovered in 1795 by scientist 'Nicholas Jacques Conte'.
• Its's density is 1.9 to 2.3 g/cm3.
• Each carbon atom is attached to three other carbon atoms forming a 'Hexagonal planar structure'.
• Free electrons move through the layers of graphite, so graphite is a good conductor of electricity.

Other allotropes of Carbon are

• It is a hard, beautiful, crystalline allotrope of carbon.
• In an atom, each carbon atom is linked to four neighbouring carbon atoms.
• These have tetrahedral three-dimensional symmetry.
• Diamond doesn't have free electrons. So. it is a non-conductor of electricity.
• Diamond is a precious stone used in jewellery.

Buckministerfullerene

• Buckminister fullerene is a stable structure of 60 carbon atoms.
• It is also known as Buckyball or just C60.
• The structure has 12 Pentagon rings and 20 hexagon rings.
• The structure is very strong and stable.

• Alkanes, Alkenes, and alkynes are the combination of carbon and hydrogen elements.
• They are commonly called hydrocarbons.
• Hydrocarbons are compounds containing carbon and hydrogen atoms.
• These hydrocarbons are present in petrol, diesel, gasoline, kerosene, lubricating oil, coal, tar, etc.
• The molecules in hydrocarbon compounds are held with each other with strong covalent sigma bonds

• On mixing the oxygen atom with the nitrogen atom, there is the formation of nitrogen dioxide (NO₂) gas.
• Oxygen and nitrogen gas both are the composition of atmospheric air.

Hydrogen and Nitrogen

• When hydrogen gas reacts with nitrogen gas there is the production of ammonia.
• Ammonia is used for various laboratory purposes.

Nitrogen and Carbon

• On mixing the nitrogen with carbon elements, Carbon nitrides are formed.
• C₃N₄ is the chemical formula of carbon nitride.

Hydrogen and oxygen

• On mixing Hydrogen and oxygen there is a formation of water, hydrogen peroxide, etc.
• H₂O and H₂O₂ are the chemical formulae of water and hydrogen peroxide.

• Examples of physical change are freezing of water, boiling of water, melting of wax, etc.
• Examples of chemical change are digestion of food, burning of paper, rusting of metal, silver tarnishing, etc.

• Physical Change:
  • When a substance undergoes a physical change, its composition remains the same despite its molecules being rearranged.
  • Physical change is a temporary change.
  • A Physical change affects only physical properties i.e. shape, size, etc.
  • A physical change involves very little to no absorption of energy.
  • Generally, physical changes do not involve the production of energy.
  • In a physical change, no new substance is formed.
  • Physical change is easily reversible that is original substance can be recovered.
• Chemical Change:
  • When a substance undergoes a chemical change, its molecular composition is changed entirely. Thus, chemical changes involve the formation of new substances.
  • A chemical change is a permanent change.
  • Chemical change both physical and chemical properties of the substance including its composition.
  • During a chemical reaction, absorption and evolution of energy take place.
  • Chemical changes usually involve the production of energy (which can be in the form of heat, light, sound, etc.).
  • A chemical change is always accompanied by one or more new substances.
  • Chemical changes are irreversible that is original substance cannot be recovered.

• The gas, which comes out on opening a soda water bottle is Carbon dioxide.
• Soda water contains carbon dioxide that has dissolved under pressure (up to 1,200 pounds per square inch).
• When the pressure is released by opening the soda container, the liquid cannot hold as much carbon dioxide, so the excess bubbles out of the solution.

• The additional carbon dioxide slowly escapes into the air if the soda is left open.
• However, under warm conditions, carbon dioxide leaves the solution faster.
• Hence, an unopened soda can is virtually bubble-free because the pressure inside the soda can keeps the carbon dioxide dissolved in the liquid.

Esters have a Fruity smell.

• Esters are produced by reacting alcohols with organic acids.
• Esters derived from carboxylic acids are the most common.
• Carboxylic acid esters, formula RCOOR′ (R and R′ are any organic combining groups), are commonly prepared by a reaction of carboxylic acids and alcohols in the presence of hydrochloric acid or sulfuric acid, a process called esterification.
• A carboxylic acid contains the -COOH group, and in an ester, the hydrogen of the Hydroxyl group is replaced by an alkyl group.
• This could be an alkyl group like methyl or ethyl, or one containing a benzene ring like phenyl.
• The term ester was introduced in the first half of the 19th century by German chemist Leopold Gmelin.

• The carbon compounds which contain only carbon and hydrogen are called hydrocarbons.
  • Among these, the saturated hydrocarbons are called alkanes. Like Methane, Ethane, etc.
  • The unsaturated hydrocarbons which contain one or more double bonds are called alkenes. Like Ethene, Butene, etc
  • Those containing one or more triple bonds are called alkynes. Like Ethyne, Propyne, etc.

Synthetic fibres:

• Synthetic fibres (man-made fibres), are fibres created by humans by chemical synthesis.
• It is different from natural fibres.
• Synthetic fibre is also made up of a series of tiny units that are linked together which form a larger unit called a polymer.
• Each little unit is made up of a chemical compound
• Rayon, Nylon, Polyester and Acrylic are examples of Synthetic.

Nylon.

• It was created in 1931 without the use of any natural raw materials (plant or animal).
• Coal, water, and air were used to make it.
• It was the world's first completely synthetic fibre.
• Nylon is a strong, elastic, and light fibre.

​Rayon.

• Rayon has properties similar to those of silk.

• It is a man-made fibre and cheaper than silk.

• It is obtained from wood pulp.

Polyester.

• Polyester is made up of many units of an ester.

• It is suitable for making dress material because it is easy to wash and stays crisp and wrinkle-free.

• Terylene is a known polyester.

• Nitric acid:
  • It ​is a strong acid with the chemical formula HNO₃.
    • Its ​PH is approximately 3.01.
  • It is also known as the spirit of nitre and aqua fortis.
    • ​Aqua fortis means strong water.
    • It is so-called because it reacts with nearly all metals.
  • ​​It is a highly corrosive and toxic acid that can cause severe skin burns.
  • It is used as a strong oxidizing agent.
  • It reacts with hydroxides, metals, and oxides to form nitrate salts.​

• ​Hydrochloric acid
  • ​It is a strong corrosive acid with a chemical formula HCl.
  • It is also known as hydrogen chloride or muriatic acid.
• ​Sulphuric acid
  • It ​is a highly corrosive, clear, colourless, odourless, strong mineral acid with the formula H₂SO₄.
  • It is also known as hydrogen sulfate.
• ​Tartaric acid
  • It ​is an organic acid found in many vegetables and fruits such as bananas, grapes, tamarinds and other citrus fruits.
  • Its chemical formula is C₄H₆O₆.

• Modern Periodic Table has 18 Groups and 7 Periods.
• It has 118 Elements.
• Each of the tables has a vertical row is called group. Elements in groups have similar chemical and physical properties because they have the same number of outer electrons.
• Each of the tables has horizontal rows is called periods. During a period, a gradual change in chemical properties occurs from one element to another.
• The elements are arranged in the modern periodic table on the basis of Mosely law, which states that the physical and chemical properties of elements are the periodic function of their atomic number.
• The Structure of it is like a bird Grid.
• The Modern Periodic table is used to organize all the known elements.
• Advantages of Modern Periodic Table:-
  • It is easier to remember the properties of an element if its position in the periodic table is known.
  • It made the study of Chemistry Systematic and Easy.

Modern Periodic Table:-

Plum pudding model​

• He proposed that an atom is made up of a positive charge and a negative charge particle in which electrons are enclosed by a positively charged cloud.
• The positive charge is uniformly distributed over the entire atom.
• The arrangement of electrons inside the continuous positive charge is similar to that of seeds in a watermelon or plums in a pudding.
• That is why Thomson's model is known as the plum-pudding model.

• As most of the alpha particles pass straight through the gold foil, so most of the space within the atom is empty.
• Rutherford suggested that all the positive charge and the mass of the atom are concentrated in a very small region, called the nucleus of the atom.
• The nucleus is surrounded by a cloud of electrons whose total negative charge is equal to the positive charge of the nucleus so that the atom as a whole is electrically neutral.

Bohr's model

• Neils Bohr put forward the following postulates about the model of an atom.
• Only certain special orbits known as discrete orbits of electrons are allowed inside the atom.
• While revolving in discrete orbits the electrons do not radiate energy.
• These orbits or shells are called energy levels.
• The energy of each stationary orbit is fixed.

• An organic acid is an organic compound with acidic properties.
• They contain one or more carboxylic acid groups, which may be covalently linked into groups such as amides, esters, and peptides.
• The most common organic acids are carboxylic acids, whose acidity is associated with their carboxyl group –COOH.

Hydroxyl (-OH):

• The Hydroxyl (-OH) functional group attached to the aliphatic carbon atom of the alkyl group forms alcohols.
• The general formula for alcohol is R-OH, where R is the alkyl group and -OH is the hydroxyl group.

Aldehydes.

• Aldehyde is a class of organic compounds, in which a carbon atom shares a double bond with an oxygen atom, a single bond with a hydrogen atom, and a single bond with another atom or group of atoms (designated R in general chemical formulas and structure diagrams).
• The double bond between carbon and oxygen is characteristic of all aldehydes and is known as the carbonyl group.
• Aldehydes are often written in the short form as R–CHO

Ketone:

• Ketones are organic compounds which incorporate a carbonyl functional group, C=O.
• The carbon atom of this group has two remaining bonds that may be occupied by alkyl group.

• Lutetium (Lu) is a chemical element with atomic number 71.
  • It is a rare earth metal of the lanthanide series of the periodic table.
  • Lutetium oxide is used to make catalysts for cracking hydrocarbons in the petrochemical industry.
  • Lu is used in cancer therapy and because of its long half-life, ¹⁷⁶Lu has been used to date the age of meteorites.

• The lanthanide or lanthanoid series of chemical elements comprises the 15 metallic chemical elements with atomic numbers 57-71, from lanthanum through the lutetium.
• Neodymium (Nd) is a chemical element with atomic number 60.
  • The most important use for Nd is in an alloy with iron and boron to make very strong permanent magnets.
• Terbium (Tb) is a chemical element with atomic number 65.
  • Tb is used to dope calcium fluoride, calcium tungstate and strontium molybdate, all used in solid-state devices.
• Cerium (Ce) is a chemical element with atomic number 58.
  • Cerium oxide is used in incandescent gas mantles, as a gas polishing agent and as a catalyst in self-cleaning ovens.

The electronic configuration is an arrangement of electrons in various

shells of an atom of an element.

Electronic configuration :

• The arrangement of electrons in the electronic levels of an atom is called its electronic configuration.
• The electrons are arranged according to their energies and space availability.
• The electrons in the completely filled shells are known as core electrons.
• The electrons that are added to the electronic shell with the highest principal quantum number are called valence electrons.

There are a few sets of rules which we follow while arranging the electrons in an atom. They are-

• Aufbau principle-
  • ​It states that the atomic orbitals which have lower energies are filled first.
  • Then the electron goes to occupy the higher atomic energy levels.
  • This ruled is followed to write the electronic configuration of atoms in their ground state.
  • When in the excited state, the electrons might vacant the lower energy state and move on to a higher energy state.
  • The order in which atomic orbitals are filled are: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p.
  • The order follows that the lower ( n + l ) value of atomic orbital will have lower energy, where n = principal quantum number and l = azimuthal quantum number.
• Pauli's exclusion principle:
  • ​An electron is characterized by four quantum numbers n, m, l, and s.
  • Pauli's exclusion principle states that every electron must have its unique set of these four quantum numbers.
  • No two electrons can have the same set of quantum numbers.
  • Simplifying, we may say that an orbital can contain a maximum of two electrons and the two electrons should have opposite spins ( + ½, - ½ ).
• Hund's rule of maximum spin multiplicity:
  • ​While filling up the orbitals of the same energy, or degeneracy, electrons will first singly occupy the subshell.
  • After each subshell has been singly occupied, electron pairing will start.
  • This rule thus implies that maximum spin should be maintained while filling up electrons in a subshell.
  • The maximum spin state involves maximum exchange energy and yields a more stable state.
• Modern periodic law:
  • ​The modern period table involves the arrangement of the elements according to their increasing Atomic number.
  • The law states that the physical and chemical properties of an element are characteristics of its Atomic number.

• Salicylic acid (C₇H₆O₃) is widely used in the cosmetic industry for its exfoliating and antiseptic properties.
• Preservatives are added to cosmetics to increase their shelf life and 2% of salicylic acid is safe to add to any cosmetic product.
• Salicylic acid is an organic compound which is colourless, bitter-tasting solid.
• An example of another preservative in cosmetics is benzyl alcohol (C₇H₈O).

• Stearic acid (C₁₈H₃₆O₂) is a saturated fatty acid with an 18-carbon chain.
  • Stearic acid is an emulsifier, emollient and lubricant that can soften skin and help to keep products from separating.
• Potassium cetyl sulfate (C₁₆H₃₄KO₄P) is a surfactant and an emulsifying agent used as a detergent and cleansing agent.
  • It is used in a variety of beauty products and cosmetics, including shampoos, facial cleansers, exfoliants, sunscreens, moisturizers and makeup removals.
• Glycerin (C₃H₈O₃) functions as a denaturant, fragrance ingredient, hair conditioning agent, humectant, oral care agent, skin protectant etc.
  • Vegetable glycerin, a clear liquid typically made from vegetable oils, is widely used in cosmetics and may offer health benefits.

• The changes in a substance or compound which brings changes in the chemical composition is called chemical changes.
• Chemical changes cannot be reversed.
  • Hence statement 2 is incorrect.
• New substances are formed in chemical changes.
  • Hence statement 1 is correct.
• Chemical changes can be endothermic or exothermic.
  • Hence statement 3 is correct.
• Chemical changes either absorb energy or release energy.

• When one chemical substance is transformed into one or more different substances, it is called a chemical change.
• The most common example is when
  • Iron transforms into rust.
  • Crystallization of sodium chloride
  • Souring of milk

• Curium (Cm) (Atomic number: 96) is made by bombarding plutonium with helium ions.
• Its compounds glow in the dark because curium is a radioactive element and therefore toxic.
• Curium has numerous applications.
  • It provides power to electrical equipment used on space missions, such as in the X-ray spectrometers in the Mars rovers.

• Copernicium (Cn) (Atomic number: 112) is a synthetic chemical element and its isotopes are extremely radioactive and have only been created in a laboratory.
  • This element was created by firing accelerated zinc-70 nuclei at a target made of lead-208 nuclei in a heavy ion accelerator.
  • Copernicium is a highly radioactive metal and is only used in research.
• Antimony (Sb) (Atomic number: 51) is a chemical element which is a lustrous grey metalloid and is mainly found in nature as the sulfide mineral stibnite.
  • Most antimony occurs in the form of more than a hundred different minerals.
  • The most important of these is stibnite, Sb₂S₃.
• Krypton (Kr) (Atomic number: 36) is a colourless, odourless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often used with other rare gases in fluorescent lamps.

• Yttrium (Y) is a chemical element with an atomic number 39.
  • Yttrium is often used as an additive in alloys.
  • It increases the strength of aluminium and magnesium alloys.
  • It is also used in the making of microwave filters for radar and has been used as a catalyst in ethene polymerisation.
  • Yttrium-aluminium garnet (YAG) is used in lasers that can cut through metals.

• Thulium (Tm) is a chemical element with atomic number 69.
  • Thulium has been used to create lasers.
• Lutetium (Lu) is a chemical element with atomic number 71.
  • Lutetium oxide is used to make catalysts for cracking hydrocarbons in the petrochemical industry.
• Erbium (Er) is a chemical element with the atomic number 68.
  • This metal is used to colour the lenses of glasses.
  • It is also used in the control rods of nuclear reactors.

• The changes that occur in a compound without changing its chemical composition is called physical changes.
• Physical changes can be reversed.
  • Hence statement 1 is incorrect.
• They occur by the change of state of matter.
  • Hence statement 4 is incorrect.
• Some of the physical changes occur by heating or cooling the substance.
  • Hence statement 2 is incorrect.
• No new product is formed in physical changes.
  • Hence statement 3 is correct.

• Physical changes affect the form of a chemical substance, but not it's the chemical composition.
• The souring of milk is classified as a chemical change because it results in the production of sour-tasting lactic acid.
• Melting of ice into water or water into water vapour changes the physical state of water hence it is classified as a physical change

• Glyceryl oleate is used in body washes.
  • It reduces the skin roughness caused by surfactants.
  • Glyceryl oleate can be found in human hair lipids.
  • Once absorbed from the hair it reduces roughness and decreases the combing force of wet hair to enhance gloss and hair quality.
• Glyceryl oleate is the ester of glycerin and oleic acid, a clear or light-coloured liquid derived from natural fats like olive, peanut or pecan oil.
  • As a non-water-soluble substance, it is ideal to emulsify substances and reduce surface tension.

• Cetrimonium bromide (C₁₉H₄₂BrN) is a quaternary ammonium surfactant.
  • It has been used as a component of DNA extraction buffer and RNA extraction buffer.
  • It is also used as a constituent of dye dissolution buffer and as a surfactant in gold nanorod preparation.
• Sodium lauryl sulfate (SLS) is an anionic surfactant commonly used as an emulsifying cleaning agent in household cleaning products like laundry detergents, spray cleaners and dishwasher detergents.
  • The chemical formula is CH₃(CH₂)₁₀CH₂(OCH₂CH₂)_NOSO₃Na.

On moving from left to right in a period the metallic character decreases.

• On moving from left to right in a period, the electrons are added into the same valence shell progressively.
• The increase in the number of electrons is paralleled by the increase in the number of protons in the nucleus.
• The effective nuclear charge is increased and the valence shell electrons are pulled strongly by electrostatic attraction. Therefore, it is difficult to give away the valence electrons, theelectropositivity is decreased and so the metallic character is also decreased. Metallic Character: The tendency to give electrons easily.

Preparation of Ketones:

• Treatment of acyl chlorides with dialkylcadmium, prepared by the reaction of cadmium chloride with Grignard reagent, gives ketones.
• When benzene or substituted benzene is treated with acid chloride in the presence of anhydrous aluminium chloride, it affords the corresponding ketone. This reaction is known as Friedel-Crafts acylation reaction.
  • Hence Friedel-Crafts acylation reaction is not used for the preparation of Aldehydes.

Preparation of Aldehydes:

• Stephen Reaction:
  • Preparation of Aldehydes from Nitriles and Esters is done by the Stephen reaction of aldehyde production.
  • The reaction was named after Henry Stephen.
• Rosenmund reaction:
  • The reduction of an acid chloride using hydrogen and a poisoned catalyst to an aldehyde is known as Rosenmund reduction.
  • The reaction was named after Karl Wilhelm Rosenmund.
• Etard reaction:
  • Chromyl chloride oxidises methyl group to a chromium complex, which on hydrolysis gives corresponding benzaldehyde.
  • This reaction is called Etard reaction.

• Picric acid (C₆H₃N₃O₇) also called 2,4,6-trinitrophenol, pale yellow, odourless crystalline solid that has been used as a military explosive, as a yellow dye, and as an antiseptic.
• Picric acid is used in the production of explosives, matches and electric batteries.
  • It is also used in etching copper and manufacturing coloured glass in the leather industry and in the synthesis of dyes.
  • Picric acid is very unstable and is a flammable/combustible material.

• Acetic acid (CH₃COOH) also known as ethanoic acid or vinegar acid is a byproduct of fermentation.
  • It is commonly used as a cleaning and disinfecting product in food processing plants.
  • Acetic acid and its sodium salt are commonly used as food preservatives.
• Oxalic acid (C₂H₂O₄) is an organic acid which is also known as ethanedioic acid.
  • It has many roles as bleach, metal polish, stain remover and mordant.
• Uric acid (C₅H₄N₄O₃) is a heterocyclic compound of carbon, nitrogen, oxygen and hydrogen.
  • Elevated uric acid levels are also associated with health conditions such as heart disease, diabetes, kidney disease etc.

Milk of Magnesia:

• Magnesia milk is an alkaline (basic) suspension of water and a creamy, suspended form of Mg(OH)₂ or magnesium hydroxide.
• It is used to neutralise excess stomach acid as an antacid.
• It is a weak base and is available in the form of liquid or tablets in medical stores.
• This is a compound formed by two ions magnesium cation and hydroxyl anion, so it is a basic compound, therefore, the pH of milk of magnesia is 10.5.
• Milk of magnesia is a medium basic compound because its pH is not so high and not so low.
• The name “milk” is used because of its milky appearance.

​Properties of Milk of Magnesia:

• The molar mass of this chemical compound is equal to 58.3197 grams per mole.
• Under standard conditions, this compound exists as a white solid that does not have any characteristic odour.
• The melting point of this compound can be approximated at 350 degrees Celsius. However, it is important to note that this compound begins undergoing decomposition at this temperature gradient.
• Milk of magnesia is not very soluble in water.
• Magnesium hydroxide crystallizes in a hexagonal crystal lattice.

• Ammonium lauryl sulfate (C₁₂H₂₉NO₄S) allows the shampoo to work through the hair more easily, giving a fresh and clean feeling.
  • This is a fat-based molecule made from coconut or palm kernel oil.
  • It is used in soaps and detergents as a foaming agent.
• Ammonium lauryl sulfate is the common name for ammonium dodecyl sulfate.
  • The anion consists of a nonpolar hydrocarbon chain and a polar sulfate end group.

• Sodium perborate (NaBO₃.nH₂O) is added to detergents as its oxidative power improves the cleaning, bleaching and stain removal performance of the detergents.
  • It is also used as a disinfectant.
• Potassium hydroxide (KOH) or caustic potash is used in a wide variety of industries like the chemical industry, mining, fertilizers etc.
  • It is used in the production of detergents due to its caustic, bleaching and drying properties.
• Sodium fluoride (NaF) toothpaste is used to prevent tooth decay.
  • It also helps to decrease the sensibility of the teeth.

• Holmium can absorb neutrons, so it is used in nuclear reactors to keep a chain reaction under contmagnetic pole piecerol.
• Holmium (Ho) is a chemical element with the atomic number 67.
• A with magnetic iron power demonstrates that holmium has the highest magnetic strength of any element.
• Holmium is used in alloys for the production of magnets.

• Europium (Eu) is a chemical element with atomic number 63.
  • Europium is useful for making control rods for nuclear reactors.
• Erbium (Er) is a chemical element with atomic number 68.
  • This metal is used to colour the lenses of glasses.
  • It is also used in the control rods of nuclear reactors.
• Dysprosium (Dy) is a chemical element with atomic number 66.
  • It is used in control rods for nuclear reactors.
  • Its compounds have been used for making laser materials and phosphor activators and in metal halide lamps.

Barium sulphate:

• BaSO₄ is an inorganic compound with the chemical name Barium Sulphate.
• Barium Sulphate is composed of a barium cation and the sulphate anion.
• The sulphur is attached to four oxygen atoms. BaSO₄ is a sulphate salt of barium and is found as the mineral barite.
• It is a crystalline solid white which is insoluble in water and alcohol but soluble in concentrated acids.
• It is odourless.
• Barium Sulphate is an alkaline, divalent metal.
• It is non-toxic and safe for medical use.
• It is widely used in the production of oil and natural gas to get high-density drilling fluids by keeping the boreholes free of rock.
• Barium is an X-ray absorber and appears white on X-ray film.
  • When instilled into the GI tract, barium coats the inside wall of the oesophagus, stomach, large intestine, and/or small intestine so that the inside wall lining, size, shape, contour, and patency (openness) are visible on X-ray.
  • Barium is used only for diagnostic studies of the GI tract.

Metallic Properties:

• Metals are good conductors of heat and electricity.
• Metals are malleable and can be easily converted into thin sheets.
• Metals are ductile, which means they can be drawn into wires.
• They produce a ringing sound, which is why they are called sonorous.
  • Hence they are used in making school bells.
• They have a very high density.
• Metals have high melting points.
• Metals are rigid solids.
• Most of the metals react with oxygen to form metal oxides.
• This is one of the reasons that metals get corroded.
• Oxides of metals are basic in nature.
• Metal oxides react with acids very easily.
• Examples of metals:- Sodium, Potassium, Calcium, Iron, etc.

Non-Metallic Properties:

• Non-metals are dull in appearance.
• They are brittle and thus, shatter when hammered.
• They are bad conductors of heat and electricity.
• They don't show the property of ductility, which means they can't be drawn into wires.
• They are not malleable or can't be changed into sheets.
• They have low densities.
• They can be solid, liquid or gas at room temperature.
• They don't produce rich sound when hit on any surface or they are not sonorous.
• Non-metals do not react with acids.
• They are generally light in weight.
• Non-metal oxides are molecular substances that form acidic solutions.
• They tend to form anions of oxyanions in an aqueous solution.
• They do not have any lustre or shine in themselves.
• Oxides of non-metals are acidic in nature.
• Non-metal oxides react with bases and form the salt.
• Examples of non-metal:- Hydrogen, Chlorine, Nitrogen, Carbon, etc.

Sublimation:

• Sublimation is defined as the transition of a substance from the solid phase to the gaseous phase without changing into the liquid phase.
• This process is an endothermic phase transition that occurs at a temperature and pressure below the triple point of the substance.
• Desublimation or deposition is the reverse of this process in which a gas is directly converted into a solid state.
• The best example of sublimation is dry ice which is a frozen form of carbon dioxide.
  • When dry ice gets exposed to air, dry ice directly changes its phase from a solid state to a gaseous state which is visible as fog.
  • Frozen carbon dioxide in its gaseous state is more stable than in its solid state.

• Another well-known example of sublimation is naphthalene which is an organic compound.
  • Naphthalene is usually found in pesticides such as mothballs.
  • This organic compound sublimes due to the presence of non-polar molecules that are held by Van Der Waals intermolecular forces.
  • At a temperature of 176°F naphthalene sublimes to form vapours. It desublimates at cool surfaces to form needle-like crystals.

• Electrical resistivity (specific electrical or volume resistivity) is a fundamental property of a material that measures how strongly it resists electric current.
• A low resistivity indicates a material that readily allows electric current.
• The insulators like rubber, paper, glass, plastics, etc. have very high resistivity compared to metallic conductors. Hence, pair 3 is correct.
• The resistivity of an alloy is generally higher than its constituent metals. Alloys do not oxidise (burn) readily at high temperatures. For this reason, they are commonly used in electrical heating devices, like electric iron, toasters etc.
  • Examples of alloys are Constantan, Manganin, Nichrome, etc. Hence, pair 2 is correct.
• Electrical conductivity or specific conductance is the reciprocal of electrical resistivity. It represents a material's ability to conduct electric current.
  • Examples of conductors include: Silver, Copper, Aluminium, Tungsten, Nickel, Iron, Chromium, Manganese, etc. Hence, pair 1 is correct.
• Resistivity and conductivity are intensive properties of materials, giving the opposition of a standard cube of material to current. Electrical resistance and conductance are corresponding extensive properties that give the opposition of a specific object to electric current.

• KCN is predominantly ionic and provides cyanide ions in solution.
• Although both carbon and nitrogen atoms are in a position to donate electron pairs, the attack takes place mainly through carbon atom and not through nitrogen atom since C—C bond is more stable than C—N bond.
• Therefore, Haloalkanes react with KCN to form alkyl cyanides as main product.
• However, AgCN is mainly covalent in nature and nitrogen is free to donate electron pair forming isocyanide as the main product.

• Nucleophiles are electron rich species. Therefore, they attack at that part of the substrate molecule which is electron deficient.
• The reaction in which a nucleophile replaces an already existing nucleophile in a molecule is called a nucleophilic substitution reaction.
• The cyanide group is a hybrid of two contributing structures and therefore can act as a nucleophile in two different ways
  • Linking through carbon atom results in alkyl cyanides
  • Linking through nitrogen atom results in isocyanides.

• Samarium (Sm) is a chemical element with atomic number 62.
• Samarium is used to dope calcium chloride crystals for use in optical lasers.
• It is also used in infrared absorbing glass and as a neutron absorber in nuclear reactors.
• Samarium oxide finds specialised use in glass and ceramics.

• Cerium (Ce) is a chemical element with atomic number 58.
  • Cerium oxide is used in incandescent gas mantles, as a glass polishing agent and as a catalyst in self-cleaning ovens.
• Terbium (Tb) is a chemical element with atomic number 65.
  • Terbium is used to dope calcium fluoride, calcium tungstate and strontium molybdate, all used in solid-state devices.
• Neodymium (Nd) is a chemical element with atomic number 60.
  • The most important use for Nd is in an alloy with iron and boron to make very strong permanent magnets.

• Aniline is used in rubber accelerators and anti-oxidants, dyes and intermediates.
• It is used to make a wide variety of products such as polyurethane foam, agricultural chemicals, stabilizers for the rubber industry etc.
• The chemical formula of aniline is C₆H5NH₂. _​

• Nitrobenzene is an organic compound which is a water-insoluble pale yellow oil with an almond-like odour.
  • ​The chemical formula is C₆H₅NO₂.
  • It is used to manufacture a chemical called aniline.
• ​Toluene (C₇H₈) is a substituted aromatic hydrocarbon.
  • ​It is used in oil refining and the manufacturing of paints.
• ​Bromobenzene (C₆H₅Br) is a colourless liquid.
  • ​It is used as a solvent and motor oil additive, and in making other chemicals.

• Aldehydes differ from ketones in their oxidation reactions.
• Ketones are generally oxidised under vigorous conditions, i.e., strong oxidising agents and at elevated temperatures. Hence option 1 is correct.
• Their oxidation involves carbon-carbon bond cleavage to afford a mixture of carboxylic acids having lesser number of carbon atoms than the parent ketone.

• Aldehydes are easily oxidised to carboxylic acids on treatment with common oxidising agents like nitric acid, potassium permanganate, potassium dichromate, etc.
• Even mild oxidising agents, mainly Tollens’ reagent and Fehlings’ reagent also oxidise aldehydes.

The mild oxidising agents given below are used to distinguish aldehydes from ketones:

• Tollens’ test:
  • On warming an aldehyde with freshly prepared ammoniacal silver nitrate solution (Tollens’ reagent), a bright silver mirror is produced due to the formation of silver metal.
  • The aldehydes are oxidised to corresponding carboxylate anion. The reaction occurs in alkaline medium.
• Fehling’s test:
  • ​Fehling reagent comprises of two solutions, Fehling solution A and Fehling solution B.
  • Fehling solution A is aqueous copper sulphate and Fehling solution B is alkaline sodium potassium tartarate (Rochelle salt).
  • These two solutions are mixed in equal amounts before test.
  • On heating an aldehyde with Fehling’s reagent, a reddish brown precipitate is obtained.
  • Aldehydes are oxidised to corresponding carboxylate anion. Aromatic aldehydes do not respond to this test.

• Liquid nitrogen has many uses, mainly based on its cold temperature and low reactivity.
• Examples of common applications include
  • The freezing and preservation of food products
  • The preservation of biological samples, such as sperm, eggs, and animal genetic sample. Hence option 1 is correct.
  • Used as a coolant for superconductors, vacuum pumps, and other materials and equipment.
  • Used cryotherapy to remove skin abnormalities.
  • The shielding of materials from the oxygen exposure
  • The quick freezing of water or pipe allow work on them when valves aren't available
  • A source of extremely dry nitrogen gas.

• Liquid helium
  • It is a physical state of helium, at very low temperatures if it is at standard atmospheric pressures. Liquid helium may show superfluidity.
  • Owing to its low melting point, liquid helium has numerous applications in cryogenics, magnetic resonance imaging (MRI), and superconducting magnets.
• Solid carbon dioxide
  • Dry ice is the solid form of carbon dioxide.
  • It is used primarily as a cooling agent but is also used in fog machines at theatres for dramatic effects.
  • Its advantages include lower temperature than that of water ice and not leaving any residue.
  • It is useful for preserving frozen foods where mechanical cooling is unavailable.
• Liquid air
  • liquefaction, change of a substance from the solid or the gaseous state to the liquid state.
  • liquid air, ordinary air that has been liquefied by compression and cooling to extremely low temperatures.

• Aspartame is commonly used as a tabletop sweetener, as a sweetener in prepared foods and beverages and in recipes that don't require too much heating (since heat breaks down aspartame).
• It can also be found as a flavouring in some medicines.
• Aspartame is an artificial sweetener whose practical use is limited to cold drinks and ice creams.
• Aspartame is an artificial non-saccharide sweetener 200 times sweeter than sucrose and is commonly used as a sugar substitute in foods and beverages.
  • It is a methyl ester of the aspartic acid/phenylalanine dipeptide with the trade names Nutrasweet, Equal and Canderel.
  • The chemical formula of aspartame is C₁₄H₁₈N₂O₅.

• Butylated hydroxyl anisole (BHA) is an antioxidant consisting of a mixture of two isomeric organic compounds, 2- tertbutyl-4-hydroxyanisole and 3- tertbutyl-4-hydroxyanisole.
  • BHA is an antioxidant and preservative in food, food packaging, animal feed, cosmetics, rubber and petroleum products.
• Sodium meta bisulphite is an inorganic compound of the chemical formula Na₂S₂O₅.
  • This is used as an antioxidant agent in many pharmaceutical formulations.
  • It is extensively used as a food preservative and disinfectant.
• Cetyl alcohol is also known as hexadecane-1ol and palmityl alcohol with the formula CH₃(CH₂)₁₅OH.
  • Cetyl alcohol acts as a binding agent, helping the various ingredients in many moisturizers, lotions and creams bind together, which helps enable the smooth application.

• Chlorophenols (C₆H₅ClO) are a group of chemicals produced by electrophilic halogenation of phenol with chlorine.
• Chlorophenols are used in a number of industries and products.
  • They can be used for making pesticides, pharmaceuticals, and dyes.
  • Some are used as disinfectants and to kill algae and fungi.

• Toluene (C₇H₈), also known as Toluol, is a substituted aromatic hydrocarbon.
  • It is used in oil refining and the manufacturing of paints, lacquers, explosives and glues.
• Phenol (C₆H₆O) is a type of organic compound.
  • It is mainly used as a disinfectant and antiseptic and in medical preparations such as mouthwash and spray cleaners.