During peptization the
A. precipitate breaks up into smaller particles of the size of a colloid
B. molecules aggregate to form a colloid
C. the precipitate adsorb one of the ions of the electrolyte on its surface
D. precipitate is shaken with the dispersion medium
E. molecules loses positive and negative charge.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A, C and D only
Peptization is the process of converting a freshly prepared precipitate into a colloidal sol by shaking it with the dispersion medium in the presence of a small amount of an electrolyte (the peptizing agent). The precipitate adsorbs one of the ions of the electrolyte, its particles all get the same charge, repel one another and break up into particles of colloidal size. For example, freshly precipitated \( \ce{Fe(OH)3} \) shaken with a little \( \ce{FeCl3} \) adsorbs \( \ce{Fe^{3+}} \) ions and forms a positively charged sol.
(A) precipitate breaks up into smaller particles of the size of a colloid — Correct. This is the result of peptization: the precipitate is dispersed into colloidal particles.
(B) molecules aggregate to form a colloid — Incorrect. Aggregation of small molecules into colloidal particles is a condensation method (e.g. multimolecular colloids), the opposite of breaking a precipitate up.
(C) the precipitate adsorb one of the ions of the electrolyte on its surface — Correct. Adsorption of a common ion gives the particles a like charge, which is what makes them separate.
(D) precipitate is shaken with the dispersion medium — Correct. The precipitate is shaken with the dispersion medium in the presence of the electrolyte.
(E) molecules loses positive and negative charge. — Incorrect. Loss of charge (neutralisation) causes coagulation, the reverse of peptization; in peptization the particles gain charge.
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):
Peptization
