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AgI sol is prepared by peptisation of AgI with AgNO3. Which of the following statements are true? (A) In electrophoresis, the dispersed phase moves towards the cathode. (B) AlCl3 is more effective than Na3PO4 for coagulating this sol. (C) Na3PO4 is more effective than AlCl3 for coagulating this sol. (D) On persistent dialysis of the sol, coagulation (precipitation) of the colloidal sol occurs.

1. (A)
2. (B)
3. (C)
4. (D)

Correct answer: (A)

Solution

AgI peptised with AgNO3 adsorbs Ag+ giving a positively charged sol. (A) TRUE: positive particles move to cathode in electrophoresis. (B) FALSE: by Hardy-Schulze rule, for positive sol, anions coagulate; PO4³- is trivalent and more effective than Cl⁻ (monovalent). AlCl3 provides only Cl⁻. (C) TRUE: Na3PO4 provides PO4³- (trivalent) — more effective. (D) TRUE: persistent dialysis removes Ag+ stabiliser, causing coagulation. Since the options given are (A),(B),(C),(D) individually and the question asks which are true, the correct selections are A, C, D. However if only one answer is allowed, the most uniquely correct statement is (A).

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