Which of the following is more effective in coagulating positively charged hydrated ferric oxide sol: (i) KCl, (ii) `CaSO_(4)`, (iii) `K_(3)[Fe(CN)_(6)]`?

Explanation

To determine which of the given substances is more effective in coagulating positively charged hydrated ferric oxide sol, we need to analyze the anions present in each option and apply Hardy-Schulze rule.

### Step-by-Step Solution:

1. **Identify the Charge of the Sol**:
- The sol in question is positively charged hydrated ferric oxide. To coagulate a positively charged sol, we need negatively charged ions (anions).

2. **List the Anions of Each Option**:
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