Which of the following is isoelectronic pair ?

Options

A. `ICl_(2),ClO_(2)`
B. `BrO_(2)^(-),BrF_(2)^(+)`
C. `ClO_(2),BrF`
D. `CN^(-),O_(3)`

Explanation

To determine which of the given pairs is isoelectronic, we need to find the total number of electrons in each species. Isoelectronic species are those that have the same number of electrons.

### Step-by-Step Solution:

1. **Identify the Species in Each Option:**
- Option 1: ICl₂ and ClO₂
- Option 2: BrO₂⁻ and BrF₂⁺
- Option 3: ClO₂ and BrF₅
- Option 4: CN⁻ and O₃

2. **Calculate the Total Electrons for Each Species:**
- **Option 1: ICl₂ and ClO₂**
- Iodine (I) has an atomic number of 53, so it has 53 electrons.
- Chlorine (Cl) has an atomic number of 17. For ICl₂, there are 2 Cl atoms:
\[ 53 + 2 \times 17 = 53 + 34 = 87 \text{ electrons} \]
- For ClO₂:
- Chlorine (Cl) = 17 electrons
- Oxygen (O) = 8 electrons, and there are 2 O atoms:
\[ 17 + 2 \times 8 = 17 + 16 = 33 \text{ electrons} \]
- Total for ICl₂ = 87, Total for ClO₂ = 33. **Not isoelectronic.**

- **Option 2: BrO₂⁻ and BrF₂⁺**
- Bromine (Br) has an atomic number of 35.
- For BrO₂⁻:
- Br = 35 electrons
- O = 8 electrons, and there are 2 O atoms:
\[ 35 + 2 \times 8 + 1 = 35 + 16 + 1 = 52 \text{ electrons} \]
- For BrF₂⁺:
- Br = 35 electrons
- F = 9 electrons, and there are 2 F atoms:
\[ 35 + 2 \times 9 - 1 = 35 + 18 - 1 = 52 \text{ electrons} \]
- Total for BrO₂⁻ = 52, Total for BrF₂⁺ = 52. **Isoelectronic pair.**

- **Option 3: ClO₂ and BrF₅**
- For ClO₂ (already calculated): 33 electrons.
- For BrF₅:
- Br = 35 electrons
- F = 9 electrons, and there are 5 F atoms:
\[ 35 + 5 \times 9 = 35 + 45 = 80 \text{ electrons} \]
- Total for ClO₂ = 33, Total for BrF₅ = 80. **Not isoelectronic.**

- **Option 4: CN⁻ and O₃**
- For CN⁻:
- C = 6 electrons
- N = 7 electrons, plus 1 extra electron due to the negative charge:
\[ 6 + 7 + 1 = 14 \text{ electrons} \]
- For O₃:
- O = 8 electrons, and there are 3 O atoms:
\[ 3 \times 8 = 24 \text{ electrons} \]
- Total for CN⁻ = 14, Total for O₃ = 24. **Not isoelectronic.**

3. **Conclusion:**
- The only isoelectronic pair is **BrO₂⁻ and BrF₂⁺**.

### Final Answer:
The isoelectronic pair is **BrO₂⁻ and BrF₂⁺**.