Which one of the following constitutes a group of the isoelectronic species

Options

A. `C_(2)^(2-),O_(2)^(-),CO,NO`
B. `NO^(+),C_(2)^(2-),CN^(-),N_(2)`
C. `CN^(-),N_(2),O_(2)^(2-),CO_(2)^(2-)`
D. `N_(2),O_(2)^(-),NO^(+),CO`

Explanation

To determine which option constitutes a group of isoelectronic species, we need to analyze the number of electrons in each species provided in the options. Isoelectronic species are those that have the same number of electrons.

### Step-by-Step Solution:

1. **Understanding Isoelectronic Species**:
- Isoelectronic species have the same number of electrons. To find them, we need to calculate the total number of electrons for each species in the given options.

2. **Analyzing the First Option (C2^2-, O2^2-, CO, NO)**:
- **C2^2-**:
- Carbon (C) has an atomic number of 6, so each carbon atom has 6 electrons.
- For two carbon atoms: 2 × 6 = 12 electrons.
- With a 2- charge, we add 2 more electrons: 12 + 2 = 14 electrons.
- **O2^2-**:
- Oxygen (O) has an atomic number of 8, so each oxygen atom has 8 electrons.
- For two oxygen atoms: 2 × 8 = 16 electrons.
- With a 2- charge, we add 2 more electrons: 16 + 2 = 18 electrons.
- **CO**:
- Carbon contributes 6 electrons and oxygen contributes 8 electrons: 6 + 8 = 14 electrons.
- **NO**:
- Nitrogen (N) has an atomic number of 7, so it has 7 electrons.
- Oxygen contributes 8 electrons: 7 + 8 = 15 electrons.
- **Conclusion for First Option**: The species C2^2- has 14 electrons, O2^2- has 18 electrons, CO has 14 electrons, and NO has 15 electrons. Since they do not all have the same number of electrons, they are not isoelectronic.

3. **Analyzing the Second Option (NO^+, C2^2-, CN^-, N2)**:
- **NO^+**:
- Nitrogen has 7 electrons and oxygen has 8 electrons: 7 + 8 = 15 electrons.
- With a +1 charge, we subtract 1 electron: 15 - 1 = 14 electrons.
- **C2^2-**:
- As calculated earlier, C2^2- has 14 electrons.
- **CN^-**:
- Carbon has 6 electrons and nitrogen has 7 electrons: 6 + 7 = 13 electrons.
- With a -1 charge, we add 1 electron: 13 + 1 = 14 electrons.
- **N2**:
- Each nitrogen atom has 7 electrons: 2 × 7 = 14 electrons.
- **Conclusion for Second Option**: NO^+ has 14 electrons, C2^2- has 14 electrons, CN^- has 14 electrons, and N2 has 14 electrons. All these species have the same number of electrons, making them isoelectronic.

4. **Final Answer**: The second option (NO^+, C2^2-, CN^-, N2) constitutes a group of isoelectronic species.