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-), C_(2)^(2-)`
D. `N_(2), O_(2)^(-), NO^(+), CO`

Answer

To determine which group of species constitutes isoelectronic species, we need to identify the total number of electrons in each species provided in the options. Isoelectronic species are defined as atoms, ions, or molecules that have the same number of electrons.

### Step-by-Step Solution:

1. **Understand the concept of isoelectronic species**:
- Isoelectronic species are those that have the same number of electrons.

2. **Analyze each option**:

**Option 1: C2²⁻, O²⁻, CO, NO**
- C2²⁻: Carbon (C) has an atomic number of 6. For C2²⁻, total electrons = 2(6) + 2 = 14.
- O²⁻: Oxygen (O) has an atomic number of 8. For O²⁻, total electrons = 2(8) + 2 = 18.
- CO: Total electrons = 6 (C) + 8 (O) = 14.
- NO: Total electrons = 7 (N) + 8 (O) = 15.
- **Conclusion**: Different number of electrons. Option 1 is incorrect.

**Option 2: NO⁺, C2²⁻, CN⁻, N2**
- NO⁺: Total electrons = 7 (N) + 8 (O) - 1 = 14.
- C2²⁻: Total electrons = 14 (as calculated above).
- CN⁻: Total electrons = 6 (C) + 7 (N) + 1 = 14.
- N2: Total electrons = 7 (N) + 7 (N) = 14.
- **Conclusion**: All have 14 electrons. Option 2 is correct.

**Option 3: CN⁻, N2, O2²⁻, C2²⁻**
- CN⁻: Total electrons = 14 (as calculated above).
- N2: Total electrons = 14 (as calculated above).
- O2²⁻: Total electrons = 2(8) + 2 = 18.
- C2²⁻: Total electrons = 14 (as calculated above).
- **Conclusion**: Different number of electrons. Option 3 is incorrect.

**Option 4: N2, O2²⁻, NO⁺, CO**
- N2: Total electrons = 14 (as calculated above).
- O2²⁻: Total electrons = 18 (as calculated above).
- NO⁺: Total electrons = 14 (as calculated above).
- CO: Total electrons = 14 (as calculated above).
- **Conclusion**: Different number of electrons. Option 4 is incorrect.

3. **Final Conclusion**:
- The only option that contains species with the same number of electrons is **Option 2: NO⁺, C2²⁻, CN⁻, N2**.

### Final Answer:
The correct group of isoelectronic species is **Option 2: NO⁺, C2²⁻, CN⁻, N2**.