Chapter 9 — Solutions: Multiple Choice Questions
Instructions: Each question carries 1 mark. Choose the best answer.
1. A solution is a ______ mixture.
Answer
(a) Heterogeneous (b) Homogeneous (c) Colloidal (d) Suspension
✅ Answer: (b) Homogeneous
ExplanationA solution is a homogeneous mixture — its composition and properties are uniform throughout. Mixtures with uneven distribution are heterogeneous. Colloids and suspensions are also mixtures but different from true solutions.
2. The substance that dissolves in a solvent to form a solution is called ______.
Answer
(a) Solvent (b) Solute (c) Mixture (d) Alloy
✅ Answer: (b) Solute
ExplanationIn a solution: Solute = substance that dissolves (present in lesser amount); Solvent = substance that does the dissolving (present in greater amount). In salt water: NaCl = solute; water = solvent.
3. Solubility of a gas in liquid ______ with increase in temperature.
Answer
(a) increases (b) decreases (c) remains the same (d) first increases then decreases
✅ Answer: (b) decreases
ExplanationDissolving a gas in liquid is exothermic. By Le Chatelier's principle, increasing temperature favors the reverse (endothermic) reaction → gas escapes from solution. That's why carbonated drinks fizz more when warm. Solubility of solids in liquids usually increases with temperature.
4. A solution that cannot dissolve any more solute at a given temperature is called ______.
Answer
(a) Unsaturated (b) Saturated (c) Supersaturated (d) Dilute
✅ Answer: (b) Saturated
Explanation
- Unsaturated: Can dissolve more solute
- Saturated: Dissolved maximum amount of solute — in equilibrium with undissolved solute
- Supersaturated: Contains more dissolved solute than normally possible (unstable, easily crystallises)
5. Which of the following is a colligative property?
Answer
(a) Boiling point (b) Elevation of boiling point (c) Colour (d) Density
✅ Answer: (b) Elevation of boiling point
ExplanationColligative properties depend only on the number of dissolved particles, not on their identity. They include:
- Elevation of boiling point (ΔTb)
- Depression of freezing point (ΔTf)
- Osmotic pressure
- Lowering of vapour pressure
6. Henry's Law states that the solubility of a gas in liquid is ______ to the pressure of gas above the liquid.
Answer
(a) inversely proportional (b) directly proportional (c) not related (d) exponentially related
✅ Answer: (b) directly proportional
ExplanationHenry's Law: The solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid at constant temperature. C = kH × P. That's why deep-sea divers get "bends" (decompression sickness) when ascending too fast — dissolved N₂ bubbles out.
7. Molarity is defined as the number of moles of solute per ______.
Answer
(a) 100 g of solvent (b) 1 kg of solvent (c) 1 litre of solution (d) 1 mole of solvent
✅ Answer: (c) 1 litre of solution
ExplanationMolarity (M) = moles of solute / volume of solution in litres. Unit: mol/L or M. It is the most commonly used concentration unit in chemistry. Note: it's per litre of solution (not solvent).
8. Which of the following liquids is the "universal solvent"?
Answer
(a) Ethanol (b) Acetone (c) Water (d) Benzene
✅ Answer: (c) Water
ExplanationWater is called the universal solvent because it dissolves more substances than any other liquid. This is due to its polar nature (dipole), ability to form hydrogen bonds, and high dielectric constant. However, it cannot dissolve non-polar substances like oils.
9. When a non-volatile solute is added to water, the boiling point of the solution ______.
Answer
(a) decreases (b) increases (c) remains the same (d) becomes 100°C exactly
✅ Answer: (b) increases
ExplanationAdding a non-volatile solute lowers the vapour pressure of the solvent (Raoult's Law). A lower vapour pressure means more energy (higher temperature) is needed to reach atmospheric pressure to boil. This is called elevation of boiling point — it is a colligative property.
10. A 10% (w/w) NaCl solution means ______.
Answer
(a) 10 g NaCl in 100 mL water (b) 10 g NaCl in 100 g solution (c) 10 mol NaCl in 100 g water (d) 10 g NaCl in 1 litre solution
✅ Answer: (b) 10 g NaCl in 100 g solution
ExplanationMass percentage (w/w) = (mass of solute / mass of solution) × 100. A 10% (w/w) solution means 10 g of solute in 100 g of solution (not 100 g of solvent). So 100 g of solution contains 10 g NaCl + 90 g water.
Quick Revision — Concentration Formulas
| Expression | Formula | Unit |
|---|
| Mass % (w/w) | (mass of solute / mass of solution) × 100 | % |
| Volume % (v/v) | (volume of solute / volume of solution) × 100 | % |
| Molarity (M) | moles of solute / volume (L) | mol/L |
| Molality (m) | moles of solute / mass of solvent (kg) | mol/kg |
| Mole fraction | moles of component / total moles | dimensionless |
📚 Samacheer Kalvi 10th Science Guide — Buy Online
