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In colloidal iron(III) hydroxide and colloidal gold, the dispersed particles carry positive and negative charges, respectively. Which of the following statements is NOT true?

1. Both sols can be coagulated by electrophoresis.
2. Combining the two sols produces no change.
3. A solution of sodium sulphate brings about coagulation in both sols.
4. Magnesium chloride causes coagulation, and it does so more readily for the gold sol than for the iron(III) hydroxide sol.

Correct answer: Combining the two sols produces no change.

Solution

Combining colloidal iron(III) hydroxide and colloidal gold does not result in any observable change because the two sols have opposite charges, which typically leads to stability rather than interaction or coagulation.

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