Which of the following electrolytes is least effective in coagulating ferric hydroxide solution?

Step-by-step solution

Fe ( OH )₃ is a positively charged sol, thus coagulated by negative ion (anion). Smaller the charge on anion, smaller is its coagulating power or higher is its flocculation value. (a) KBr K ⁺+ Br ⁻ (b) K ₂ SO ₄ 2 ~K ⁺+ SO ₄ ²⁻ (c) K ₂ CrO ₄ 2 ~K ⁺+ CrO ₄ ²⁻ (d) K ₄ [ Fe ( CN )₆ ] 4 ~K ⁺+ [ Fe ( CN )₆ ]⁴⁻ Br ⁻ has smaller charge. KBr is least effective in coagulating Fe ( OH )₃ sol.