50. Which of the following is NOT an example of a colloid?
[RRB Group D, 25 Aug 2026, Shift 2]
(A) Milk
(B) Blood
(C) Sugar solution
(D) Ice cream
Answer: (C) Sugar solution
Explanation: A sugar solution is a true homogeneous solution: individual sugar molecules are distributed throughout water and are too small to produce appreciable Tyndall scattering. Milk and ice cream are colloidal systems; blood contains dispersed components and colloidal plasma constituents.
49. Which of the following is a characteristic of a true solution?
[RRB Group D, 25 Aug 2026, Shift 1]
(A) Solute particles are easily separated by filtration
(B) Solute particles can be seen with the naked eye
(C) Solute particles settle rapidly at the bottom
(D) Solute particles are evenly distributed in the solution
Answer: (D) Solute particles are evenly distributed in the solution
Explanation: A true solution has a uniform composition because dissolved particles spread throughout its solvent. The particles are molecular or ionic in size, do not settle on standing and pass through ordinary filter paper. Salt dissolved in water is a familiar example.
48. Which of the following is a property of a suspension?
[RRB Group D, 21 Aug 2026, Shift 3]
(A) Its particles never settle down
(B) It is a homogeneous mixture
(C) Its particles are smaller than 1 nm
(D) It can be separated by filtration
Answer: (D) It can be separated by filtration
Explanation: A suspension contains comparatively large, undissolved particles distributed in a fluid. These particles can settle when undisturbed and are retained by ordinary filter paper. Muddy water illustrates the distinction between a suspension, a colloid and a true solution.
47. Which of the following is a correct property of a colloidal solution?
[RRB Group D, 18 Aug 2026, Shift 1]
(A) The solute settles at the bottom after some time
(B) The particles scatter a beam of light
(C) The dispersed particles are separated by ordinary filtration
(D) All colloidal particles are visible to the naked eye
Answer: (B) The particles scatter a beam of light
Explanation: Colloidal particles are large enough to scatter incident light, producing the Tyndall effect. Unlike the larger particles in a suspension, they generally remain dispersed instead of settling quickly. Ordinary filter paper cannot normally separate the dispersed colloidal phase from its medium.
46. What are the two main components of a colloidal solution?
[RRB Group D, 17 Aug 2026, Shift 2]
(A) Metal phase and non-metal medium
(B) Reactant phase and product medium
(C) Dispersed phase and dispersion medium
(D) Solute phase and solvent medium
Answer: (C) Dispersed phase and dispersion medium
Explanation: The dispersed phase consists of fine particles distributed throughout the continuous dispersion medium. For example, in milk, tiny fat droplets form part of the dispersed phase while the surrounding aqueous liquid acts as the medium. Their states determine the colloid type.
45. Which of the following is a chemical change and NOT a physical change?
[RRB Group D, 12 Aug 2026, Shift 3]
(A) Melting of ice
(B) Rusting of iron
(C) Dissolving sugar in water
(D) Boiling of water
Answer: (B) Rusting of iron
Explanation: Iron reacts with oxygen in the presence of moisture and forms hydrated iron oxides known as rust. Since a new material results, rusting is chemical. Melting, boiling and the ordinary dissolution of sugar alter physical state or distribution without forming new compounds.
44. Which of the following is an example of a homogeneous mixture?
[RRB Group D, 10 Aug 2026, Shift 2]
(A) Sand and water
(B) Sugar dissolved in water
(C) Oil and water
(D) Iron filings and sulfur
Answer: (B) Sugar dissolved in water
Explanation: Dissolved sugar molecules spread uniformly throughout water, giving a single-phase mixture with essentially identical composition in every small sample. Sand and water remain a suspension, while oil and water separate into layers. Mixed iron filings and sulfur are also heterogeneous.
43. Which of the following statements is NOT correct?
[SSC GD Constable, 29 May 2026, Shift 2]
(A) Evaporation causes heating
(B) The states of matter are interconvertible
(C) Boiling is a bulk phenomenon
(D) Evaporation is a surface phenomenon
Answer: (A) Evaporation causes heating
Explanation: Evaporation normally causes cooling, not heating, because escaping molecules take energy from the liquid and its surroundings. Boiling occurs throughout a liquid at its boiling temperature under a given pressure. Evaporation can occur at the surface over a range of temperatures.
42. What is the amount of solute present in a given amount of solution known as?
[SSC MTS, 18 Feb 2026, Shift 3]
(A) Dilution
(B) Saturation
(C) Concentration
(D) Diffusion
Answer: (C) Concentration
Explanation: Concentration describes how much solute is present relative to a specified mass or volume of solution. It may be expressed as a mass percentage, molarity or another suitable unit. Dilution lowers concentration by adding solvent; saturation describes a solubility limit.
41. Why do we feel cool after applying water to our skin in summer?
[RRB ALP CBT-I, 17 Feb 2026, Shift 2]
(A) Evaporation absorbs heat from the skin surface
(B) Water raises body temperature by absorbing sunlight
(C) Condensation releases energy onto the skin
(D) Water stops sweating and traps body heat
Answer: (A) Evaporation absorbs heat from the skin surface
Explanation: To evaporate, water molecules need energy to escape into the gaseous state. They absorb this energy partly from the skin, which loses heat and feels cooler. The process is a physical change; water remains chemically H2O before and after evaporation.