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Solutions CBSE Class 12 MCQ & Practice Questions

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Solutions Revision Guide for CBSE Class 12 Chemistry

Solutions deals with concentration terms, vapour pressure and colligative properties. Many exam questions are short numericals where correct units and interpretation are more important than lengthy calculation.

For CBSE Class 12 Chemistry, revise mole fraction, molarity, molality, Raoult law, ideal and non-ideal behaviour, elevation of boiling point, depression of freezing point and osmotic pressure.

Important Topics

  • Concentration terms
  • Raoult law
  • Ideal and non-ideal solutions
  • Colligative properties
  • van’t Hoff factor
  • Osmotic pressure

Important Formulae & Relationships

  • Molarity M = moles of solute / volume of solution (L)
  • Molality m = moles of solute / mass of solvent (kg)
  • ΔTb = iKb m
  • ΔTf = iKf m
  • π = iCRT

Use formulas only after checking the required units, sign convention and assumptions for the question.

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CBSE Class 12 Chemistry · Solutions · Very Very Hard

1. Positive deviation from Raoult's law occurs when A–B interactions are:

  • A. Stronger than A–A and B–B
  • B. Weaker than A–A and B–B
  • C. Exactly equal
  • D. Ionic only
Answer: B
Explanation: Weaker unlike interactions allow molecules to escape more readily, increasing vapour pressure.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

2. Negative deviation from Raoult's law occurs when A–B interactions are:

  • A. Weaker
  • B. Stronger
  • C. Absent
  • D. Purely repulsive
Answer: B
Explanation: Stronger unlike interactions lower escaping tendency and vapour pressure.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

3. Raoult's law for a volatile component is:

  • A. pᵢ = xᵢpᵢ°
  • B. pᵢ = pᵢ°/xᵢ
  • C. pᵢ = xᵢ/pᵢ°
  • D. pᵢ = RT/xᵢ
Answer: A
Explanation: Partial vapour pressure equals mole fraction times vapour pressure of the pure component.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

4. An ideal solution obeys Raoult's law:

  • A. Only at low concentration
  • B. Over the entire composition range
  • C. Only at high pressure
  • D. Only at 0°C
Answer: B
Explanation: Ideal solutions obey Raoult's law throughout the full composition range.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

5. Molarity is defined as:

  • A. Moles of solute per kg solvent
  • B. Moles of solute per litre solution
  • C. Grams of solute per litre solvent
  • D. Moles of solvent per litre solution
Answer: B
Explanation: Molarity is the number of moles of solute per litre of solution.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

6. The sum of mole fractions in a solution is:

  • A. 0
  • B. 1
  • C. 10
  • D. Depends on temperature
Answer: B
Explanation: The mole fractions of all components in a mixture add up to one.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

7. For an ideal solution, enthalpy of mixing is:

  • A. Positive
  • B. Negative
  • C. Zero
  • D. Infinite
Answer: C
Explanation: Ideal mixing produces no heat effect, so ΔHmix = 0.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

8. For an ideal solution, volume change on mixing is:

  • A. Positive
  • B. Negative
  • C. Zero
  • D. Always 1 L
Answer: C
Explanation: Ideal solutions show ΔVmix = 0.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

9. A minimum-boiling azeotrope shows:

  • A. Positive deviation
  • B. Negative deviation
  • C. No deviation
  • D. No vapour pressure
Answer: A
Explanation: Positive deviation raises vapour pressure and lowers boiling point.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

10. A maximum-boiling azeotrope shows:

  • A. Positive deviation
  • B. Negative deviation
  • C. Ideal behaviour
  • D. No intermolecular force
Answer: B
Explanation: Negative deviation lowers vapour pressure and raises boiling point.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

11. Relative lowering of vapour pressure for a dilute non-volatile solute equals:

  • A. Mole fraction of solvent
  • B. Mole fraction of solute
  • C. Molality
  • D. Molarity
Answer: B
Explanation: For dilute solutions, (p°−p)/p° = xsolute.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

12. Elevation in boiling point is given by:

  • A. ΔTb = Kbm
  • B. ΔTb = Kf/m
  • C. ΔTb = m/Kb
  • D. ΔTb = RT
Answer: A
Explanation: Boiling-point elevation is proportional to molality.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

13. Depression in freezing point is given by:

  • A. ΔTf = Kfm
  • B. ΔTf = Kbm
  • C. ΔTf = m/Kf
  • D. ΔTf = RT
Answer: A
Explanation: Freezing-point depression is proportional to molality.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

14. Osmotic pressure is given by:

  • A. π = CRT
  • B. π = C/RT
  • C. π = RT/C
  • D. π = Kbm
Answer: A
Explanation: For dilute solutions, osmotic pressure follows the van't Hoff equation π = CRT.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

15. Reverse osmosis is used for:

  • A. Increasing vapour pressure
  • B. Desalination of water
  • C. Preparing azeotropes
  • D. Measuring viscosity
Answer: B
Explanation: Applying pressure greater than osmotic pressure forces solvent through a semipermeable membrane.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

16. The van't Hoff factor i accounts for:

  • A. Temperature change only
  • B. Association or dissociation of solute
  • C. Solvent colour
  • D. Pressure units
Answer: B
Explanation: i corrects colligative properties for changes in the number of solute particles.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

17. Molality is defined as:

  • A. Moles of solute per kg solvent
  • B. Moles of solute per litre solution
  • C. Grams of solute per litre solution
  • D. Moles of solvent per kg solute
Answer: A
Explanation: Molality is the number of moles of solute per kilogram of solvent.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

18. Which concentration term is independent of temperature?

  • A. Molarity
  • B. Molality
  • C. Normality
  • D. Volume percent
Answer: B
Explanation: Molality depends on masses, which do not vary with temperature.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

19. According to Henry's law, gas solubility generally increases with:

  • A. Decreasing pressure
  • B. Increasing pressure
  • C. Increasing temperature always
  • D. Removing solvent
Answer: B
Explanation: Higher gas pressure increases the dissolved mole fraction.

CBSE Class 12 Chemistry · Solutions · Very Very Hard

20. Gas solubility in liquids generally decreases with:

  • A. Increasing pressure
  • B. Decreasing temperature
  • C. Increasing temperature
  • D. Adding inert gas at constant partial pressure
Answer: C
Explanation: Dissolution of gases is usually exothermic, so heating reduces solubility.

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Solutions Practice Tests

Solutions Frequently Asked Questions

Which concentration unit is temperature independent?

Molality is based on mass of solvent and therefore does not change with temperature, unlike molarity which depends on solution volume.

Why is the van’t Hoff factor used?

It accounts for association or dissociation of solute particles so that observed colligative properties can be related to the effective number of dissolved particles.

How can I improve accuracy in Solutions numericals?

Convert masses, volumes and molecular masses carefully, write the chosen concentration unit explicitly and check whether association or dissociation affects the particle count.

Continue with another chapter to build connected concepts and strengthen your overall Chemistry preparation.

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