Thermally most stable compound is:

Options

A. `HOClO_(3)`
B. `HOClO_(2)`
C. `HOCl`
D. `HOClO`

Explanation

To determine which of the given compounds is the thermally most stable, we need to analyze the thermal stability of the oxoacids of chlorine provided in the options. The compounds are:

1. HOClO3 (Perchloric acid)
2. HOClO2 (Chloric acid)
3. HOCl (Hypochlorous acid)
4. HOClO (Chlorous acid)

### Step-by-Step Solution:

**Step 1: Understand Thermal Stability**
- Thermal stability of a compound is influenced by the bond strength and bond length of the bonds present in the molecule. Stronger bonds tend to provide greater stability against thermal decomposition.

**Hint:** Remember that bond strength and bond length are inversely related; stronger bonds have shorter lengths.

**Step 2: Identify the Oxidation States**
- The oxidation states of chlorine in the given compounds are:
- HOCl: +1
- HOClO: +3
- HOClO2: +5
- HOClO3: +7

**Hint:** Higher oxidation states typically lead to stronger bonds due to increased positive charge on chlorine.

**Step 3: Analyze Bond Strength**
- The bond strength of the Cl-O bond increases with the oxidation state of chlorine. The bond strengths for the compounds are as follows:
- HOCl: 209 kJ/mol
- HOClO: 240.5 kJ/mol
- HOClO2: 243.7 kJ/mol
- HOClO3: 263.5 kJ/mol

**Hint:** Higher bond strength indicates greater thermal stability.

**Step 4: Compare Bond Strengths**
- From the bond strength data, we can see that:
- HOClO3 has the highest bond strength (263.5 kJ/mol).
- This indicates that HOClO3 (Perchloric acid) has the strongest Cl-O bond among the given compounds.

**Step 5: Conclusion**
- Since HOClO3 has the highest bond strength, it is the thermally most stable compound among the options provided.

**Final Answer:** The thermally most stable compound is **HOClO3 (Perchloric acid)**.