In which of the following, oxidation number of chloride is `+5` ?

Options

A. `Cl_2O_7`
B. `ClO_3^-`
C. `ClO^-`
D. `ClO_4^-`

Answer

To determine in which of the given compounds the oxidation number of chloride (Cl) is +5, we will analyze each option systematically.

### Step-by-Step Solution:

1. **Identify the Compounds**: We need to analyze the oxidation state of chlorine in each of the following compounds:
- A) Cl₂O₇
- B) ClO₃⁻
- C) ClO₂
- D) ClO₄⁻

2. **Calculate Oxidation Number for Cl₂O₇**:
- Let the oxidation number of Cl be \( x \).
- The oxidation number of O is -2.
- The equation for the compound is:
\[ 2x + 7(-2) = 0 \]
- Simplifying gives:
\[ 2x - 14 = 0 \implies 2x = 14 \implies x = +7 \]
- Therefore, the oxidation number of Cl in Cl₂O₇ is +7.

3. **Calculate Oxidation Number for ClO₃⁻**:
- Let the oxidation number of Cl be \( x \).
- The equation for the compound is:
\[ x + 3(-2) = -1 \]
- Simplifying gives:
\[ x - 6 = -1 \implies x = -1 + 6 \implies x = +5 \]
- Therefore, the oxidation number of Cl in ClO₃⁻ is +5.

4. **Calculate Oxidation Number for ClO₂**:
- Let the oxidation number of Cl be \( x \).
- The equation for the compound is:
\[ x + 2(-2) = 0 \]
- Simplifying gives:
\[ x - 4 = 0 \implies x = +4 \]
- Therefore, the oxidation number of Cl in ClO₂ is +4.

5. **Calculate Oxidation Number for ClO₄⁻**:
- Let the oxidation number of Cl be \( x \).
- The equation for the compound is:
\[ x + 4(-2) = -1 \]
- Simplifying gives:
\[ x - 8 = -1 \implies x = -1 + 8 \implies x = +7 \]
- Therefore, the oxidation number of Cl in ClO₄⁻ is +7.

6. **Conclusion**: From the calculations:
- Cl₂O₇: +7
- ClO₃⁻: +5
- ClO₂: +4
- ClO₄⁻: +7

The only compound where the oxidation number of chloride is +5 is **ClO₃⁻**. Thus, the correct answer is **Option B**.