Electrical disintegration or Bredig's Arc method involves:

The correct answer is Option (2) → Condensation

In Bredig’s arc method an electric arc is struck between electrodes of the metal (gold, silver, platinum) dipped in the dispersion medium. The intense heat vaporises the metal, and the vapour then condenses to form particles of colloidal size. The process thus involves dispersion as well as condensation, and the step that actually forms the colloidal particles is condensation.

Why the other options are incorrect

• Option (1) Fermentation — Incorrect. Fermentation is the breakdown of organic substances by enzymes; no enzyme or organism is involved in the arc method.

• Option (3) Evaporation — Incorrect. The metal is vaporised by the arc, but evaporation alone gives no colloid; the vapour has to condense into colloidal particles.

• Option (4) Filtration — Incorrect. Filtration separates particles; it does not form a sol.

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):
Electrical Disintegration or Bredig’s Arc Method – “This process involves dispersion as well as condensation. Colloidal sols of metals such as gold, silver, platinum, etc., can be prepared by this method. In this method, electric arc is struck between electrodes of the metal immersed in the dispersion medium. The intense heat produced vapourises the metal, which then condenses to form particles of colloidal size.”