Chemistry MCQ Questions with Answer for all Competitive Exams

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Chemistry MCQ Questions with Answer

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Q1. Atomic theory‘ of the matter was given by

(a) Avogadro

(b) Dalton

(c) Newton

(d) Pascal

Answer: (b)

Explanation: Atomic theory of matter was given by John Dalton. According to this theory, matter is made up of extremely small indivisible and indestructible particles called Atoms.

Q2. An ideal gas is one that obeys ​

(a) ​Gas laws ​

(b) ​Boyle’s laws ​

(c) ​Charle’s law ​

(d)​ Avogadro’s law

Answer: (a)​

Explanation: A gas, when kept at a constant temperature, would obey the gas laws exactly. The gas laws are Charle’s law, Boyle’s law, and Gay-Lussac’s law.

Q3. The nucleus of an atom consists of.

(a) Proton

(b) Neutron

(c) Proton and Neutron

(d) Electron, Proton and Neutron

Answer: (c)

Explanation: All atoms except the hydrogen atom, are composed of three fundamental particles, namely electrons, protons, and neutrons. Protons and neutrons are present inside the nucleus.

Q4. Which one of the following can be used to confirm whether drinking water contains a gamma-emitting isotope or not?

(a) Microscope

(b) Lead plate

(c) Scintillation counter

(d) Spectrophotometer

Answer: (c)

Explanation: Scintillation counter (scintillometer): An instrument that measures gamma radiation. It is also used in airborne and ground radiometer surveys. This instrument utilizes the flash of light emitted when the atoms of a suitable ‘ phosphor’ are energized by gamma rays. The scintillations are detected by a light-sensitive cathode.

Q5. Which gas is responsible for the swelling of bread? ​

(a) ​Oxygen

​(b) ​Carbon monoxide

​(c) ​Carbon dioxide ​

(d)​ Ammonia

Answer: ​(c)​

Explanation: Carbon dioxide is responsible for the swelling of bread.

Q6. LPG is a mixture of ​

(a)​ C6H12 + C6H6

(b) ​C4H10 + C3H8

(c)​ C2H2 + C2H4

(d)​ CH4 + C2H4

Answer: (b)​

Explanation: LPG is a mixture of C4H10 (Butane), C3H8 (propane) and C2H6 (ethane). Main constituent is butane (C4H10).

Q7. When the Helium atom loses an electron, then it becomes–

(a) Proton

(b) Positive Helium ion

(c) Negative Helium ion

(d) Alpha Particle

Answer: (b)

Explanation: When the Helium atom loses an electron, then it forms a positive helium ion.

He →He+ +e

Also Read: Physics MCQ Questions  with Answer for all Competitive Exams

Q8.Yellowcake’, an item of smuggling across the border is

(a) A crude form of heroin

(b) A crude form of cocaine

(c) Uranium oxide

(d) Unrefined gold

Answer: (c)

Explanation: Uranium oxide is smuggled across borders in the form of yellowcake. Uranium oxide is produced by refining tons of dirt (ore) containing uranium to produce “Yellowcake“. Typically yellow cake contains 80% of uranium oxide, which melts at approximately 2878°C whereas modern yellow cake contains 70 to 90% triuranium oxide (U3O8) by weight. Yellowcake is used in the preparation of uranium fuel for the nuclear reactor. Uranium obtained from yellowcake is also used in making many types of illegal nuclear explosives which is very dangerous to mankind.

Q9. Which of the following is a radioactive element?

(a) Cobalt

(b) Uranium

(c) Argon

(d) Chromium

Answer: (b)

Explanation: Elements having atomic no. greater than 82 are radioactive in nature. In the given options, the Atomic Number of Uranium is 92 so, it is a radioactive element.

Q10. The — OH group of — COOH can be replaced by Cl using

(a) PCl5

(b) HOCl

(c) Cl2

(d) HCl

Answer: (a)

Explanation: The -OH group of -COOH can be replaced by Cl using PCl5, PCl3 or SOCl2. In the given options PCl5 is the correct answer.

Q11. The gas used in the manufacture of Vanaspati Ghee from Vanasapati Oil is –

(a) Hydrogen

(b) Oxygen

(c) Nitrogen

(d) Carbon dioxide

(e) None of the above / more than one of the above

Answer: ​(a)​

Explanation: Vanaspati ghee is manufactured from vegetable oil by a process called ‘hydrogenation. Bypassing hydrogen gas. Vegetable Oil contains unsaturated fatty acids; upon hydrogenation, it is converted into saturated fatty acids to form vanaspati ghee.

Q12. The Discovery of the nucleus of an atom was due to an experiment carried out by ​

(a)​ Bohr ​

(b)​ Rutherford

​(c)​ Moseley ​

(d) ​Thomson

Answer: (b)​

Explanation: Rutherford determined that the particles that made up the gold foil must consist mostly of empty space since most of the alpha particles passed through. However, some regions of the gold must have been too dense to allow the alpha particles through, and this heavy part of the atom was what Rutherford called the nucleus. He concluded that it was the nucleus that held most of the atom’s mass.

Q13. The chemical used as a ‘fixer’ in photography is

(a) Sodium sulfate

(b) Sodium thiosulphate

(c) Ammonium persulphate

(d) Borax

Answer: (b)

Explanation: Sodium thiosulphate is used in photography as a fixer. It removes Ag from the negative by dissolving unexposed silver bromide resulting in the formation of the complex.

AgBr + 2Na2S2O3   → Na3 [Ag (S2O3)2] + NaBr

Q14. Match the following pair:-

NatureSubstance
1. Acidic(a) Distill water
2. Basic(b) Carbonated drink
3. Neutral(c) Soap

(a) 1 – a, 2 – c, 3 – b

(b) 1 – b, 2 – c, 3 – a

(c) 1 – a, 2 – b, 3 – c

(d) 1 – c, 2 – a, 3 – b

Answer: (b)

Explanation:

1. Acidic → Carbonated drink
2. Basic → Soap
3. Neutral → Distil water

The carbonated drink is Acidic in nature due to the presence of H2CO3 acid. Soaps are Sodium or Potassium salts of fatty acids, which provide basic nature. Distil water has no salts or impurity so it is neither acidic nor basic i.e. neutral.

Q15. What is the common name of Calcium Hypochlorite?

(a) Water

(b) Bleaching powder

(c) Baking soda

(d) Baking powder

Answer: (b)

Explanation: Calcium Hypochlorite is a bleaching powder. Its chemical formula is CaOCl2. It is used in the disinfection of water and as a bleaching agent.

Q16. The atoms, in which the number of protons is the same but the number of neutrons is different, are known as

(a) ​Isotopes ​

(b) ​Isobars

​(c)​ Isomers

​(d) ​Isotones

Answer: ​(a)​

Explanation: In isotopes electrons and protons are found in equal Numbers white the number of neutrons is different.

Q17. The strength of hydrogen bonding in O, F, S, Cl, and N is in the order:

(a) Cl < S < N < O < F

(b) Cl < F < S < N < O

(c) Cl < N < S < O < F

(d) Cl < O < S < N < F

Ans. (a)

Explanation: Strength of a Hydrogen bonding, H……M increases with the increase in the electronegativity of M–atom. Out of the given atoms, Cl– does not form H–bond while the strength of H-bonding of other atoms is in the order S <N < O < F, since the electronegativity of these atoms also increases in the same order S (2.5) < N (3.0) < O (3.5) < F (4.0)

Q18. What happens when one and one p orbital is hybridized?

(a) We get three orbital in a plane

(b) We get two orbital at 180 degrees

(c) We get two mutually perpendicular orbital

(d) We get four orbital directed tetrahedral

Answer: (b)

Explanation: Molecular orbital (MO) Theory was developed by F. Hund R.S. Mulliken in 1932. According to this theory – The number of molecular orbitals formed is equal to the number of combining orbitals. When two atomic orbital combine, two molecular orbitals is formed.

Q19. Match List-I with List-II and select the correct answer using the codes given below the lists:

List-IList-II
A. German silver1. Tin
B. Solder2. Nickel
C. Bleaching powder3. Sodium
D. Hypo4. Chlorine

Codes:

(a) A-1; B-2; C-4; D-3

(b) A-2; B-1; C-3; D-4

(c) A-1; B-2; C-3; D-4

(d) A-2; B-1; C-4; D-3

Answer: (d)

Explanation: German silver has a colour resembling silver, but is an alloy of primarily copper, nickel, and zinc. Solder is an alloy of tin, antimony, copper, and lead. Bleaching powder contains calcium chloride and calcium hypochlorite, used in solution as a bleach. Bleaching powder is sold on the basis of available chlorine, which is liberated when it is treated with dilute acid. It is used for bleaching paper pulps and fabrics and for sterilizing water. The Hypo solution used in iodometric titration is sodium thiosulphate (Na2S2O3).

Q20. Oils are purified by ​

(a)​ Fractional distillation

​(b)​ Steam distillation

​(c)​ Crystallization

​(d)​ Vacuum distillation

Answer: (b)​

Explanation: Oils are purified by steam distillation. In the steam distillation process, steam is bubbled through a heated mixture of raw material. Some of the target components will vaporize which are coded and condensed yielding a layer of oil and a layer of water.

Q21. Which one among the following equations is correctly balanced? ​

(a)​ NaOH + Al + H2O → 2H2 + NaAlO2

(b)​ 2NaOH + 2Al + 2H2O → 3H2 + 2NaAlO2

(c)​ 2NaOH + 2Al + 3H2O → 4H2 + 2NaAlO2

(d)​ 2NaOH + 2Al + H2O → H2 + 2NaAlO2

Answer: (b)​

Explanation: As per the law of conservation of mass, of reactant atom on the right side of a chemical equation must be equal to the no of elements on the left side such an equation is called a balanced chemical equation.

Q22. What are Rubies and Sapphires chemically known as?

(a) Silicon dioxide

(b) Aluminium oxide

(c) Lead tetroxide

(d) Boron nitride

Answer: (b)

Explanation: Rubies and Sapphires are scientifically the same stone, differing only in colour. Corundum, the predominating mineral of both, is composed of nearly pure alumina (Al2O3). The colouring substance which differentiates rubies and sapphires is believed to be chromium.

Q23. Benzene is ______ in ethyl alcohol.

(a) Soluble

(b) Solute

(c) Insoluble

(d) Insolate

Answer: (c)

Explanation: Polar molecules are soluble in polar solvents while non-polar molecules are soluble in non-polar solvents. Benzene is a non-polar molecule while ethyl alcohol is a polar solvent so it is insoluble in ethyl alcohol.

Q24. Helium gas is filled in the balloon instead of Hydrogen because its–

(a) Lighter than Hydrogen

(b) More abundant than Hydrogen

(c) Non-Combustible

(d) More stable

Answer: (c)

Explanation: Because it is a non-combustible (non-flammable) gas.

Q25. The rusting of iron nail ​

(a)​ Decreases its weight ​

(b)​ Increases its weight

​(c)​ Does not affect weight but iron is oxidized ​

(d)​ Does not affect weight but iron is reduced

Answer: (b)​

Explanation: The rusting of the iron nail takes place in the presence of air (oxygen) and water (moisture). It increases the weight of the iron nail due to the formation of rust. ​​

4Fe + 3O2 + xH2O → 2Fe2O3.xH2O (rust)

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