Which of the following species absorb maximum energy in its `HOMO-LUMO` electronic transition?

Options

A. `O_(2)`
B. `N_(2)^(-)`
C. `C_(2)`
D. `N_(2)`

Answer

To determine which of the given species absorbs the maximum energy in its HOMO-LUMO electronic transition, we need to analyze the molecular orbitals of each species and identify the energy gap between the Highest Occupied Molecular Orbital (HOMO) and the Lowest Unoccupied Molecular Orbital (LUMO).

### Step-by-Step Solution:

1. **Identify the Species**: The species given in the question are O2, N2-, C2, and N2.

2. **Draw Molecular Orbitals**:
- **O2**: The molecular orbital configuration for O2 is:
- σ(1s)², σ*(1s)², σ(2s)², σ*(2s)², σ(2p)², π(2p)², π*(2p)²
- Total electrons = 8 (2p4)
- HOMO = π*(2p) (antibonding)
- LUMO = σ*(2p) (antibonding)

- **N2-**: The molecular orbital configuration for N2- is:
- σ(1s)², σ*(1s)², σ(2s)², σ*(2s)², σ(2p)², π(2p)², π*(2p)²
- Total electrons = 7 (2p3 + 1 extra electron)
- HOMO = π*(2p) (antibonding)
- LUMO = σ*(2p) (antibonding)

- **C2**: The molecular orbital configuration for C2 is:
- σ(1s)², σ*(1s)², σ(2s)², σ*(2s)², σ(2p)², π(2p)²
- Total electrons = 4 (2p2)
- HOMO = π(2p) (bonding)
- LUMO = σ(2p) (bonding)

- **N2**: The molecular orbital configuration for N2 is:
- σ(1s)², σ*(1s)², σ(2s)², σ*(2s)², σ(2p)², π(2p)²
- Total electrons = 6 (2p3)
- HOMO = σ(2p) (bonding)
- LUMO = π*(2p) (antibonding)

3. **Determine Energy Gaps**:
- The energy gap between HOMO and LUMO is crucial for determining the energy absorbed during the electronic transition.
- For O2: Energy gap = π*(2p) to σ*(2p)
- For N2-: Energy gap = π*(2p) to σ*(2p)
- For C2: Energy gap = π(2p) to σ(2p)
- For N2: Energy gap = σ(2p) to π*(2p)

4. **Compare Energy Gaps**:
- The largest energy gap corresponds to the transition from σ(2p) (bonding) to π*(2p) (antibonding) in N2, which is greater than the gaps in the other species.
- The transitions in O2 and N2- are also significant, but the transition in N2 has the largest energy difference.

5. **Conclusion**:
- The species that absorbs the maximum energy in its HOMO-LUMO electronic transition is **N2**.

### Final Answer:
**N2** absorbs the maximum energy in its HOMO-LUMO electronic transition.