Of the four oxyacids of chlorine the strongest oxidising agent in dilute aqueous solution is :

Explanation

To determine which of the four oxyacids of chlorine is the strongest oxidizing agent in dilute aqueous solution, we need to analyze the oxidation states of chlorine in each oxyacid. The four oxyacids of chlorine are:

1. **HClO4** (Perchloric acid)
2. **HClO3** (Chloric acid)
3. **HClO2** (Chlorous acid)
4. **HOCl** (Hypochlorous acid)

### Step-by-Step Solution:

**Step 1: Determine the oxidation state of chlorine in HClO4.**
- The formula for oxidation state calculation:
\[ \text{Oxidation state of Cl} + 1 + (-2) \times 4 = 0 \]
\[ \text{Oxidation state of Cl} + 1 - 8 = 0 \implies \text{Oxidation state of Cl} = +7 \]

**Step 2: Determine the oxidation state of chlorine in HClO3.**
- Using the same formula:
\[ \text{Oxidation state of Cl} + 1 + (-2) \times 3 = 0 \]
\[ \text{Oxidation state of Cl} + 1 - 6 = 0 \implies \text{Oxidation state of Cl} = +5 \]

**Step 3: Determine the oxidation state of chlorine in HClO2.**
- Again using the formula:
\[ \text{Oxidation state of Cl} + 1 + (-2) \times 2 = 0 \]
\[ \text{Oxidation state of Cl} + 1 - 4 = 0 \implies \text{Oxidation state of Cl} = +3 \]

**Step 4: Determine the oxidation state of chlorine in HOCl.**
- Using the formula:
\[ \text{Oxidation state of Cl} + 1 + (-2) = 0 \]
\[ \text{Oxidation state of Cl} + 1 - 2 = 0 \implies \text{Oxidation state of Cl} = +1 \]

**Step 5: Compare the oxidation states.**
- The oxidation states of chlorine in the acids are:
- HClO4: +7
- HClO3: +5
- HClO2: +3
- HOCl: +1

**Step 6: Identify the strongest oxidizing agent.**
- The strongest oxidizing agent is the one that can achieve the highest oxidation state and has the greatest tendency to reduce itself. Since HClO4 has the highest oxidation state of +7, it can reduce to +5, +3, or +1, making it the strongest oxidizing agent among the four.

### Final Answer:
The strongest oxidizing agent in dilute aqueous solution among the four oxyacids of chlorine is **HClO4** (Perchloric acid).