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Solutions WBCHSE Class 12 MCQ & Practice Questions

Practice Solutions MCQs for WBCHSE Class 12 Chemistry with answers, explanations, chapter revision and related ChemNexa mock tests.

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Solutions Revision Guide for WBCHSE 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 WBCHSE 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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WBCHSE Class 12 Chemistry · Solutions · Very Hard

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

  • A. Stronger than both pure-component interactions
  • B. Ionic only
  • C. Identical to pure interactions
  • D. Weaker than A-A and B-B interactions
Answer: D
Explanation: Weaker unlike interactions increase escaping tendency and vapour pressure.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

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

  • A. Absent
  • B. Always repulsive
  • C. Stronger than A-A and B-B interactions
  • D. Weaker than pure interactions
Answer: C
Explanation: Stronger unlike interactions lower escaping tendency.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

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

  • A. pi=xi pi°
  • B. pi=pi°/xi
  • C. pi=xi/pi°
  • D. pi=xi+pi°
Answer: A
Explanation: Partial vapour pressure equals liquid mole fraction times pure vapour pressure.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

4. For an ideal binary solution of volatile liquids, total vapour pressure is:

  • A. pA-pB
  • B. pA pB
  • C. pA/pB
  • D. pA+pB
Answer: D
Explanation: Dalton's law gives total pressure as the sum of partial pressures.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

5. An ideal solution obeys Raoult's law:

  • A. Only at x=1
  • B. Never
  • C. Over the entire composition range
  • D. Only at x=0
Answer: C
Explanation: Ideal solutions follow Raoult's law at all compositions.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

6. Relative lowering of vapour pressure for a dilute nonvolatile solute equals approximately:

  • A. Molality squared
  • B. Molar mass of solvent
  • C. Mole fraction of solute
  • D. Mole fraction of solvent
Answer: C
Explanation: Raoult's law gives (p°-p)/p° = xsolute.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

7. Elevation of boiling point is expressed as:

  • A. ΔTb=Kb/m
  • B. ΔTb=Kb m
  • C. ΔTb=Kf m
  • D. ΔTb=m/Kb
Answer: B
Explanation: For dilute solutions boiling-point elevation is proportional to molality.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

8. Osmotic pressure of a dilute solution is given by:

  • A. π=C/RT
  • B. π=RT/C
  • C. π=CR/T
  • D. π=CRT
Answer: D
Explanation: The van't Hoff equation for dilute solutions is π=CRT.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

9. For a nonvolatile solute, addition to a solvent generally:

  • A. Makes vapour pressure zero always
  • B. Lowers vapour pressure
  • C. Raises vapour pressure above pure solvent necessarily
  • D. Leaves vapour pressure unchanged
Answer: B
Explanation: The solvent mole fraction decreases, lowering its vapour pressure.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

10. Which colligative property is especially useful for molar masses of macromolecules?

  • A. Freezing-point depression only
  • B. Vapour pressure of pure solid
  • C. Osmotic pressure
  • D. Boiling-point elevation only
Answer: C
Explanation: Osmotic pressure is measurable even for very dilute macromolecular solutions.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

11. Two solutions having equal osmotic pressure at the same temperature are:

  • A. Azeotropic
  • B. Isotonic
  • C. Hypertonic
  • D. Hypotonic
Answer: B
Explanation: Isotonic solutions have equal osmotic pressure.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

12. A solution with greater osmotic pressure than another is:

  • A. Hypertonic
  • B. Hypotonic
  • C. Isotonic
  • D. Ideal
Answer: A
Explanation: Higher effective solute-particle concentration gives greater osmotic pressure.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

13. A solution with lower osmotic pressure than another is:

  • A. Hypertonic
  • B. Isotonic
  • C. Azeotropic
  • D. Hypotonic
Answer: D
Explanation: Lower effective solute concentration gives lower osmotic pressure.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

14. Molarity is defined as:

  • A. Moles of solute per litre of solution
  • B. Moles of solute per kg solvent
  • C. Mass solute per litre solvent
  • D. Moles solvent per litre solution
Answer: A
Explanation: Molarity is n/V(solution in L).

WBCHSE Class 12 Chemistry · Solutions · Very Hard

15. For a binary solution, the sum of mole fractions is:

  • A. Depends on temperature
  • B. 1
  • C. 0
  • D. 2
Answer: B
Explanation: All mole fractions in a mixture sum to unity.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

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

  • A. Infinite
  • B. Zero
  • C. Always positive
  • D. Always negative
Answer: B
Explanation: Intermolecular interactions are effectively unchanged on mixing.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

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

  • A. Zero
  • B. Always positive
  • C. Always negative
  • D. Equal to solvent volume
Answer: A
Explanation: Ideal mixing has no volume contraction or expansion.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

18. Depression of freezing point is expressed as:

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

WBCHSE Class 12 Chemistry · Solutions · Very Hard

19. Reverse osmosis requires application of pressure:

  • A. Less than osmotic pressure
  • B. Greater than osmotic pressure
  • C. Less than vapour pressure only
  • D. Exactly zero
Answer: B
Explanation: Pressure exceeding osmotic pressure reverses solvent flow.

WBCHSE Class 12 Chemistry · Solutions · Very Hard

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

  • A. Solvent colour
  • B. Atmospheric pressure only
  • C. Density of container
  • D. Association or dissociation of solute
Answer: D
Explanation: i corrects colligative properties for changed particle number.

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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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