Chemistry MCQ Questions with Answer for all Competitive Exams

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Chemistry MCQ Questions with Answer

 

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 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 color. Corundum, the predominating mineral of both, is composed of nearly pure alumina (Al2O3). The coloring 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)

Q26. The metal constituent of chlorophyll is ​

(a)​ Iron ​

(b) ​Potassium ​

(c) ​Manganese ​

(d)​ Magnesium

Answer: (d)​

Explanation: Chlorophyll is a green pigment in which at the centre of the ring is a magnesium ion. It also bears a long phytol chain.

Q27. Match List-I (Industrial process) with List-II (Industry with which associated) and select the correct answer using the codes given below the lists:

List-I (Industrial process)List-II (Industry with which associated)
A. Cracking1. Rubber
B. Smelting2. Petroleum
C. Hydrogenation3. Copper
D. Vulcanization4. Edible fats

Codes:

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

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

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

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

Answer: (b)

Explanation: Cracking is the process whereby complex organic molecules such as kerosene or heavy hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds.

Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. In this process the oxide ore is reduced to free metal by using reducing agents like coke or charcoal. Copper is also obtained from its oxide by this method in Free State.

Hydrogenation is a reduction reaction which results in an addition of hydrogen (usually as H2). If an organic compound is hydrogenated, it becomes more ‘saturated’. Hydrogenation results in the conversion of liquid vegetable oils to solid (edible) fats.

Vulcanization is a chemical process for converting rubber into more durable materials via the addition of sulfur. Sulfur modifies the rubber by forming cross-links (bridges) between individual polymer chains. Vulcanized material is less sticky and has superior mechanical properties.

Q28. Why Helium gas used in balloons?

(a) Its atomic number is two

(b) Its Lighter than air

(c) It’s one of the constituents of water

(d) It’s a noble gas

Answer: (b)

Explanation: Helium gas is lighter than air and non-flammable (non-combustible) so it is used in balloons.

Q29. What is used to prevent the freezing of fuel in space crafts?

(a) Benzene

(b) Glycol

(c) Acetylene

(d) Ester

Answer: (b)

Explanation: Ethylene Glycol is used to prevent the freezing of fuel in space crafts.

Q30. The tracking of people by trained dogs is based on the recognition of which of the following compounds in the sweat from feet?​​

​(a)​ Carboxylic acids

​(b) ​Uric acid

​(c) ​Sugar ​

(d)​ Salt

Answer: (a)​

Explanation: The tracking of people by trained dogs is based on the recognition of carboxylic acid in sweat from feet.

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