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Practice MCQ Question for Class 12 Chemistry chapter-wise

1. The atmospheric pollution is generally measured in the units of

(a) mass percentage
(b) volume percentage
(c) volume fraction
(d) ppm

2. 234.2 gm of sugar syrup contains 34.2 gm of sugar. What is the molal concentration of the solution

(a) 0.1
(b) 0.5
(c) 5.5
(d) 55

3. Atomic mass is equal to

(a) number of electrons of an atom
(b) sum of the numbers of electrons and protons of an atom
(c) sum of the numbers of neutrons and protons of an atom
(d) none of these

4. The law which indicates the relationship between solubility of a gas in liquid and pressure is

(a) Raoult’s law
(b) Henry’s law
(c) Lowering of vapour pressure
(d) Van’t Hoff law

5. Among the following substance the lowest vapour pressure is exerted by

(a) water
(b) alcohol
(c) ether
(d) mercury

6. Partial pressure of a solution component is directly proportional to its mole fraction. This is known as

(a) Henry’s law
(b) Raoult’s law
(c) Distribution law
(d) Ostawald’s dilution law

7. Which of the following solutions shows positive deviation from Raoult’s law?

(a) Acetone + Aniline
(b) Acetone + Ethanol
(c) Water + Nitric acid
(d) Chloroform + Benzene

8. The system that forms maximum boiling azeotrope is

(a) Acetone-chloroform
(b) ethanol-acetone
(c) n-hexane-n-heptane
(d) carbon disulphide-acetone

9. A plant cell shrinks when it is kept in a

(a) hypotonic solution
(b) hypertonic solution
(c) isotonic solution
(d) pure water

10. The relative lowering in vapour pressure is proportional to the ratio of number of

(a) solute molecules to solvent molecules
(b) solvent molecules to solute molecules
(c) solute molecules to the total number of molecules in solution
(d) solvent molecules to the total number of molecules in solution

11. The osmotic pressure of a solution can be increased by

(a) increasing the volume
(b) increasing the number of solute molecules
(c) decreasing the temperature
(d) removing semipermeable membrane

12. Sprinkling of salt helps in clearing the snow covered roads in hills. The phenomenon involved in the process is

(a) lowering in vapour pressure of snow
(b) depression in freezing point of snow
(c) melting of ice due to increase in temperature by putting salt
(d) increase in freezing point of snow

13. For carrying reverse osmosis for desalination of water the material used for making semipermeable membrane is

(a) potassium nitrate
(b) parchment membrane
(c) cellulose acetate
(d) cell membrane

14. What will be the degree of dissociation of 0.1 M Mg(NO₃)₂ solution if van’t Hoff factor is 2.74?

(a) 75%
(b) 87%
(c) 100%
(d) 92%

15. Which of the following units is useful in relating concentration of solution with its vapour pressure?

(a) Mole fraction
(b) Parts per million
(c) Mass percentage
(d) Molality

16. At equilibrium the rate of dissociation of a solid solute in a volatile liquid solvent is

(a) less than the rate of crystallisation
(b) greater than the rate of crystallisation
(c) equal to the rate of crystallisation
(d) zero

17. If molality of the dilute solution is doubled, the value of molal depression constant (K_f) will be?

(a) doubled
(b) halved
(c) tripled
(d) unchanged

18. Temperature dependent term among the following is -

(a) Molality
(b) Molarity
(c) Mole fraction
(d) Weight percentage

19. An aqueous solution is 1.00 molal in KI. Which change will cause the vapour pressure of the solution to increase?

(a) Addition of NaCl
(b) Addition of Na₂SO₄
(c) Addition of 1.00 molal KI
(d) Addition of water

20. A solution of acetone in ethanol is-

(a) Shows a negative deviation from Raoult's law
(b) Shows a positive deviation from Raoult's law
(c) Behaves like a near ideal solution
(d) Obeys Raoult's law

21. The mixture that forms maximum boiling azeotrope is-

(a)  Heptane + Octane
(b)  Water + Nitric acid
(c)  Ethanol  + Water
(d) Acetone + Carbon disulfide

22. Isotonic solutions have same-

(a) Vapour pressure
(b) Freezing temperature
(c) Osmotic pressure
(d) Boiling temperature 

23. Among the following options, 0.1 M aqueous solution will have the lowest freezing point is-

(a) Potassium Sulphate
(b) Sodium chloride
(c) Urea
(d) Glucose

24. A two phase system consisting of a liquid dispersed in another liquid is known as-

(a) Foam 
(b) Suspension
(c) Emulsion
(d) Mist

25. The van't Hoff factor [i] for a dilute aqueous solution of the strong electrolyte barium hydroxide is?

(a) 0
(b) 1
(c) 2
(d) 3

Answer :

1. Answer : (d) ppm

Explanation: Since the amount of pollutants present in the atmosphere is very small, atmospheric pollution is measured in parts per million (ppm).

2.Answer : (b) 0.5

Explanation: Weight of water in sugar syrup 

= 234.2 − 34.2

= 200gm

Molecular weight of sugar = 342

Molal concentration \(=\frac{34.2}{342}\times\frac{1000}{200}\)​

​​​​​Molal concentration = 0.5

3. Answer : (b) sum of the numbers of electrons and protons of an atom

Explanation: The atomic mass of an atom is an empirically measured property, which is equivalent to the sum mass of protons, neutrons, and electrons that make up the atom (with a small adjustment for nuclear binding energy).

4. Answer : (b) Henry’s law

Explanation: Henry's Law is the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.

5. Answer : (d) mercury

Explanation: Mercury exerts the lower vapour pressure because of the strong bond among its atom.

6. Answer : (b) Raoult’s law

Explanation: The relationship is known as the Raoult's law which states that for a solution of volatile liquids, the partial vapour pressure of each component of the solution is directly proportional to its mole fraction present in solution.

7. Answer : (b) Acetone + Ethanol

Explanation: Acetone + ethanol is an example of solutions showing positive deviation from Raoult's law.

8. Answer : (a) Acetone-chloroform

Explanation: acetone – chloroform is a non-ideal solution and has a negative deviation. It is a maximum boiling azeotrope.

9. Answer : (b) hypertonic solution

Explanation: Hypertonic solution has high osmotic pressure. When a plant cell is placed in hypertonic solution water will diffuse out of the cell resulting in shrinking of the cell.

10.Answer : (c) solute molecules to the total number of molecules in solution

Explanation: Relative lowering of vapour pressure.  The vapour pressure of a liquid is the pressure of the vapour which is in equilibrium with that liquid. The vapour pressure of a solvent is lowered when a non-volatile solute is dissolved in it to form a solution.

11. Answer : (b) increasing the number of solute molecules

Explanation: The osmotic pressure of a solution increases as the number of solute molecules increases. Excess pressure produced on the solution side owing to osmosis is known as osmotic pressure. The osmotic pressure of a solution increases as the number of solute molecules increases.

12. Answer : (b) depression in freezing point of snow

Explanation: When salt is spread over snow covered roads, snow starts melting from the surface because depression of freezing point of water takes place due to addition of salt. It helps in clearing of roads. Hence, the phenomena is depression in freezing point which helps in clearing the snow covered roads in hilly areas.

13.Answer : (c) cellulose acetate

Explanation: Cellulose acetate, potassium ferrocyanide, etc. are used as semipermeable membrane for carrying out reverse osmosis.

14. Answer : (b) 87%

Explanation: \(Mg(NO_3)_2\longrightarrow\)​ \(Mg^{2+}+2NO^-_3\)​

\(\alpha=\frac{i-1}{n-1}\)

\(=\frac{2.74-1}{3-1}\)​

\(=\frac{1.74}{2}\)​

​​​​​​= 0.87

Degree of Dissociation 

= 0.87(100)

= 87%

15. Answer : (a) Mole fraction

Explanation: Mole fraction is useful in relating vapour pressure with concentration of solution. According to Raoult's law, the partial vapour pressure of each component in the solution is directly proportional to its mole fraction.

16. Answer : (c) equal to the rate of crystallisation

Explanation: This means that the rate of crystallisation is equal to the rate of the dissolution for a solid solute in a volatile liquid. At equilibrium the rate of dissolution will be equal to the rate of crystallisation.

17. Answer : (d) unchanged

Explanation: If the molality of a dilute solution is doubled, the value of the molal depression constant (K_f) remains unchanged. Because molal depression is constantly dependent on the nature of the solvent, not on solute.

18. Answer : (b) Molarity

Explanation: molarity is the concentration term which is temperature dependent.

19. Answer : (d) Addition of water

Explanation: However, the addition of solvent, ie, dilution increases the surface area of the liquid surface, thus results in increased vapour pressure. Hence, the addition of water to the aqueous solution of (1 molal) KI, result in increased vapour pressure.

20. Answer : (b) Shows a positive deviation from Raoult's law

Explanation: A solution of acetone in ethanol shows a positive deviation from Raoult's law due to miscibility of these two liquids with a difference of polarity and length of the hydrocarbon chain.

21. Answer : (b)  Water + Nitric acid

Explanation: The mixture that forms maximum boiling azeotrope is water and nitric acid. This mixture of water and nitric acid shows negative deviation from Roult's law and it will form maximum boiling azeotrope.

22. Answer : (c) Osmotic pressure

Explanation: An isotonic solution is a solution that has the same osmolarity or solute concentration as another solution. 

23. Answer : (a) Potassium Sulphate

Explanation: Urea and glucose do not dissociate in solution. Sodium chloride gives two ions and potassium sulphate gives three ions per formula unit. Therefore, the effective number of particles is maximum in potassium sulphate. Hence, its freezing point is lowest.

24. Answer : (c) Emulsion

Explanation: An emulsion is a mixture of two or more liquids that are normally immiscible (unmixable or unblendable) owing to liquid-liquid phase separation. Emulsions are part of a more general class of two-phase systems of matter called colloids.

25. Answer : (d) 3

Explanation: Ba(OH)₂ is a strong electrolyte, so its 100% dissociation occurs in solution. 

Van't off factor(i) = Total number of ions present in the solution.

\(Ba(OH)_2\longrightarrow \) \(Ba^{2+}+2OH^-\)

​​​​​​So, the total number of ions in the solution is 3.

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