Chemistry MCQ Questions with Answer for all Competitive Exams

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.

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.

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.

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.

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

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

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

He →He⁺ +e^–

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.

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.

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.

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.

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.

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

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.

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.

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

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)

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.

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).

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.

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.

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.

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.

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

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)