Which of the following statements are true? A. Flocculation value is…

The correct answer is Option (4) → A, B, C, D only

Note 1: The given answer is as per the official NTA Answer Key. However, the correct answer should be Option (1), as explained below.

A lyophobic sol is coagulated by ions of the opposite charge. A lyophilic sol added to a lyophobic sol can protect it from coagulation.

• (A) Flocculation value is inversely proportional to the coagulating power. — True. The flocculation (coagulating) value is the minimum concentration of electrolyte needed to coagulate the sol. The greater the coagulating power of an ion, the smaller the amount needed, so the lower its flocculation value.

• (B) Colloidal silicon is a protective colloid. — As per NTA it is correct. However, this statement is not correct. A protective colloid is a lyophilic sol, such as gelatin, gum or starch: its particles form a layer around the lyophobic particles and protect them from electrolytes. Colloidal silicon is a sol of an element, of the same kind as the sols of metals, so it is a lyophobic sol. It needs protection itself and cannot protect another sol. So statement (B) should have been false, which leaves A, C and D only, i.e. Option (1).

• (C) Alum is used for cleaning muddy water. — True. The particles in muddy water are negatively charged; the \( \ce{Al^{3+}} \) ions of alum neutralise them, so they coagulate and settle.

• (D) Gelatin is added to ice-cream to act as an emulsifier. — True. Gelatin is a lyophilic colloid; it stabilises the fat-in-water emulsion of ice-cream and keeps it smooth.

Note 2: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Protection of Colloids

Coagulation or Precipitation – …

Applications of Colloids – …