Class 12 Chemistry MCQ Worksheet Chapter 1 Solutions | Detailed Solutions & Marking Scheme

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 VEDANT WORKSHEET SERIES

Class: 12
Subject: Chemistry
Chapter: 1 – Solutions
Time: 1 Hour
Maximum Marks: 30

SECTION A

MCQs (1 × 15 = 15 Marks)

Q1. Which of the following represents a solid in liquid solution?
A. Sugar in water
B. Air
C. Brass
D. Hydrogen in palladium

Q2. The molarity of a solution prepared by dissolving 5 g NaOH in 500 mL solution is:
A. 0.25 M
B. 0.5 M
C. 0.1 M
D. 1 M

Q3. Which concentration term is independent of temperature?
A. Molarity
B. Molality
C. Normality
D. Formality

Q4. According to Henry’s law, solubility of gas in liquid is:
A. Directly proportional to temperature
B. Inversely proportional to pressure
C. Directly proportional to pressure
D. Independent of pressure

Q5. Which of the following is a colligative property?
A. Density
B. Vapour pressure
C. Osmotic pressure
D. Viscosity

Q6. Raoult’s law is applicable to:
A. Non-ideal solutions only
B. Ideal solutions only
C. Electrolytes only
D. Colloids only

Q7. When a non-volatile solute is added to a solvent, vapour pressure:
A. Increases
B. Decreases
C. Remains same
D. First increases then decreases

Q8. Elevation in boiling point depends upon:
A. Nature of solute
B. Number of solute particles
C. Nature of solvent only
D. Temperature only

Q9. The unit of molality is:
A. mol L⁻¹
B. mol kg⁻¹
C. g L⁻¹
D. mol m⁻³

Q10. Which solution shows positive deviation from Raoult’s law?
A. Benzene + Toluene
B. Acetone + Chloroform
C. Ethanol + Water
D. Hexane + Heptane

Q11. Depression in freezing point is proportional to:
A. Temperature
B. Pressure
C. Molality
D. Volume

Q12. Osmotic pressure is given by:
A. π = CRT
B. π = MRT
C. π = nRT
D. π = PRT

Q13. Van’t Hoff factor (i) for NaCl (ideal case) is:
A. 1
B. 2
C. 3
D. 0

Q14. Abnormal molar mass arises due to:
A. Association or dissociation
B. High temperature
C. Low pressure
D. Impurities only

Q15. Which method is used for determination of molar mass of macromolecules?
A. Elevation in boiling point
B. Depression in freezing point
C. Osmotic pressure
D. Vapour pressure lowering

Assertion-Reason Questions (1 × 15 = 15 Marks)

Q16. Assertion (A): Molality is preferred over molarity in colligative properties.
Reason (R): Molality is independent of temperature.

Q17. Assertion (A): Ideal solutions obey Raoult’s law at all concentrations.
Reason (R): Intermolecular forces between components are equal.

Q18. Assertion (A): Solubility of gases decreases with increase in temperature.
Reason (R): Dissolution of gases is exothermic.

Q19. Assertion (A): Relative lowering of vapour pressure is a colligative property.
Reason (R): It depends on number of solute particles.

Q20. Assertion (A): Electrolytes show abnormal molar mass.
Reason (R): They dissociate into ions in solution.

Q21. Assertion (A): Osmotic pressure is directly proportional to temperature.
Reason (R): π = CRT

Q22. Assertion (A): Positive deviation occurs when A–B interactions are weaker.
Reason (R): Vapour pressure increases in such solutions.

Q23. Assertion (A): Colligative properties depend on nature of solute.
Reason (R): They depend on number of particles.

Q24. Assertion (A): Depression in freezing point increases with molality.
Reason (R): ΔTf = Kf × m

Q25. Assertion (A): Van’t Hoff factor is always greater than 1.
Reason (R): Solute always dissociates.

Q26. Assertion (A): Henry’s constant increases with temperature.
Reason (R): Gas solubility decreases with temperature.

Q27. Assertion (A): Molarity changes with temperature.
Reason (R): Volume of solution changes with temperature.

Q28. Assertion (A): Non-ideal solutions show deviation from Raoult’s law.
Reason (R): Interactions between molecules differ.

Q29. Assertion (A): Osmosis occurs from dilute to concentrated solution.
Reason (R): Solvent moves through semi-permeable membrane.

Q30. Assertion (A): Association leads to decrease in colligative properties.
Reason (R): Number of particles decreases.

Answer Options for Questions 16–30:
A. Both A and R are true, R is correct explanation of A
B. Both A and R are true, R is not correct explanation of A
C. A is true, R is false
D. A is false, R is true

DETAILED ANSWER KEY – VEDANT WORKSHEET SERIES (CLASS 12 CHEMISTRY – SOLUTIONS)

SECTION A – MCQs

Q1. A. Sugar in water
Solid (solute) dissolved in liquid (solvent) → solid in liquid solution

Q2. A. 0.25 M
Moles = 5/40 = 0.125 mol
Volume = 0.5 L
M = 0.125 / 0.5 = 0.25 M

Q3. B. Molality
Molality depends on mass, not volume → independent of temperature

Q4. C. Directly proportional to pressure
Henry’s Law: p ∝ x (solubility increases with pressure)

Q5. C. Osmotic pressure
Depends only on number of particles → colligative property

Q6. B. Ideal solutions only
Raoult’s law strictly valid for ideal solutions

Q7. B. Decreases
Non-volatile solute lowers vapour pressure

Q8. B. Number of solute particles
Colligative property → depends on particles

Q9. B. mol kg⁻¹
Molality = moles of solute / kg of solvent

Q10. C. Ethanol + Water
Shows positive deviation due to weaker interactions

Q11. C. Molality
ΔTf ∝ m

Q12. A. π = CRT
C = molarity

Q13. B. 2
NaCl → Na⁺ + Cl⁻

Q14. A. Association or dissociation
Changes number of particles

Q15. C. Osmotic pressure
Best method for macromolecules (proteins, polymers)

SECTION A – ASSERTION-REASON

Q16. A
Both true, correct explanation

Q17. A
Equal intermolecular forces → ideal behavior

Q18. A
Gas dissolution is exothermic → solubility decreases

Q19. A
Depends on number of solute particles

Q20. A
Electrolytes dissociate → abnormal molar mass

Q21. A
π = CRT → directly proportional to T

Q22. A
Weaker A–B → higher vapour pressure

Q23. D
A is false, R is true
(Colligative properties do NOT depend on nature)

Q24. A
ΔTf = Kf × m → directly proportional

Q25. D
A is false, R is true
(i can be <1 in association)

Q26. A
As T ↑ → solubility ↓ → KH ↑

Q27. A
Volume changes → molarity changes

Q28. A
Different interactions → deviation

Q29. B
Both true but R not full explanation

Q30. A
Association ↓ number of particles → lowers effect

MARKING INSIGHT (CBSE EXAM STRATEGY)

  • 22–25 marks → Excellent conceptual clarity

  • 18–21 marks → Good, revise numericals & AR logic

  • <18 marks → Focus on colligative properties + formulas

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