Which one of the following electrolytes will have maximum coagulating…

The correct answer is Option (3) → \(Al_2(SO_4)_3\)

A sol is coagulated by the ion of the added electrolyte that carries the charge opposite to that of the sol particles. By the Hardy–Schulze rule, the greater the valence of this coagulating ion, the greater its coagulating power.

AgI/\( \ce{I^{-}} \) is a negative sol, so it is coagulated by cations. Among the given electrolytes the cations are \( \ce{Na^{+}} \) (NaCl, \( \ce{Na2SO4} \)), \( \ce{Ba^{2+}} \) and \( \ce{Al^{3+}} \):

So Al₂(SO₄)₃, with the trivalent \( \ce{Al^{3+}} \), has the maximum coagulating power.

Why the other options are incorrect

• Option (1) \(NaCl\) — Incorrect. \( \ce{Na^{+}} \) has charge +1, the weakest coagulating ion here.

• Option (2) \(Ba(NO_3)_2\) — Incorrect. \( \ce{Ba^{2+}} \) has charge +2, weaker than \( \ce{Al^{3+}} \).

• Option (4) \(Na_2SO_4\) — Incorrect. Its cation is again \( \ce{Na^{+}} \); the \( \ce{SO4^{2-}} \) ion has the same sign as the sol and does not coagulate it.

Note: 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):
Coagulation or Precipitation – …