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Select the correct statement(s) regarding colloidal systems. (I) TiO2 sol, chalk sol, dioxin sol, Sb2S3 sol and Ag sol are all examples of charged sols. (II) The electric double layer on colloidal particles provides stability to the sol. (III) Continuous electrolysis can cause coagulation of a sol. (IV) Proteins, gum and lamp black are emulsifiers for oil-in-water (o/w) emulsions.

1. Only I and II
2. Only II and III
3. Only I, II and III
4. Only II, III and IV

Correct answer: Only II and III

Solution

Statement II is correct: the electric double layer creates a repulsive potential (zeta potential) that prevents particle aggregation. Statement III is correct: continuous electrolysis moves counter-ions away, collapsing the double layer and causing coagulation. Statement IV is incorrect because lamp black stabilizes w/o emulsions, not o/w emulsions (proteins and gums do stabilize o/w, but lamp black does not). Statement I is partially misleading — not all listed sols carry the same sign of charge, and 'critically charged' is not a standard classification.

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