Which of the follwing is/are isoelectronic species ?

Options

A. `NCN^(2-)`
B. `CO_(2)`
C. `N_(3^(-))`
D. `OCN^(-)`

Explanation

To determine which of the given species are isoelectronic, we need to calculate the total number of electrons for each species. Isoelectronic species are those that have the same number of electrons.

### Step-by-Step Solution:

1. **Identify the species**: We have the following species to analyze:
- \( \text{N} \text{C} \text{N}^{2-} \)
- \( \text{CO}_2 \)
- \( \text{N}^{3-} \)
- \( \text{OCN}^{-} \)

2. **Calculate the number of electrons for each species**:
- **For \( \text{N} \text{C} \text{N}^{2-} \)**:
- Nitrogen (N) has 7 electrons. There are 2 Nitrogens: \( 2 \times 7 = 14 \)
- Carbon (C) has 6 electrons: \( 6 \)
- The \( 2- \) charge adds 2 electrons.
- Total: \( 14 + 6 + 2 = 22 \) electrons.

- **For \( \text{CO}_2 \)**:
- Carbon (C) has 6 electrons: \( 6 \)
- Each Oxygen (O) has 8 electrons. There are 2 Oxygens: \( 2 \times 8 = 16 \)
- Total: \( 6 + 16 = 22 \) electrons.

- **For \( \text{N}^{3-} \)**:
- Nitrogen (N) has 7 electrons.
- The \( 3- \) charge adds 3 electrons.
- Total: \( 7 + 3 = 10 \) electrons.

- **For \( \text{OCN}^{-} \)**:
- Oxygen (O) has 8 electrons: \( 8 \)
- Carbon (C) has 6 electrons: \( 6 \)
- Nitrogen (N) has 7 electrons: \( 7 \)
- The \( - \) charge adds 1 electron.
- Total: \( 8 + 6 + 7 + 1 = 22 \) electrons.

3. **Compare the total number of electrons**:
- \( \text{N} \text{C} \text{N}^{2-} \): 22 electrons
- \( \text{CO}_2 \): 22 electrons
- \( \text{N}^{3-} \): 10 electrons
- \( \text{OCN}^{-} \): 22 electrons

4. **Determine which species are isoelectronic**:
- The species \( \text{N} \text{C} \text{N}^{2-} \), \( \text{CO}_2 \), and \( \text{OCN}^{-} \) all have 22 electrons.
- \( \text{N}^{3-} \) has only 10 electrons and is not isoelectronic with the others.

### Conclusion:
The isoelectronic species among the given options are \( \text{N} \text{C} \text{N}^{2-} \), \( \text{CO}_2 \), and \( \text{OCN}^{-} \).

### Final Answer:
The isoelectronic species are \( \text{N} \text{C} \text{N}^{2-} \), \( \text{CO}_2 \), and \( \text{OCN}^{-} \).

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