Which of the following contain maximum number of electrons in the antibonding molecular orbitals

Answer

To determine which of the given species contains the maximum number of electrons in the antibonding molecular orbitals, we will follow these steps:

### Step 1: Identify the number of electrons for each species
- **O2^2-**: 18 electrons
- **O2**: 16 electrons
- **O2^-**: 17 electrons
- **O2-O2**: 17 electrons

### Step 2: Understand the molecular orbital filling order
The order of filling molecular orbitals for diatomic molecules is as follows:
1. σ 1s
2. σ* 1s
3. σ 2s
4. σ* 2s
5. σ 2p_z
6. π 2p_x = π 2p_y
7. π* 2p_x = π* 2p_y
8. σ* 2p_z

### Step 3: Fill the molecular orbitals for each species
1. **O2^2- (18 electrons)**:
- σ 1s: 2
- σ* 1s: 2
- σ 2s: 2
- σ* 2s: 2
- σ 2p_z: 2
- π 2p_x: 2
- π 2p_y: 2
- π* 2p_x: 2
- π* 2p_y: 2
- **Total in antibonding (σ* and π*): 2 (σ*) + 2 (σ*) + 2 (π*) + 2 (π*) = 8 electrons**

2. **O2 (16 electrons)**:
- σ 1s: 2
- σ* 1s: 2
- σ 2s: 2
- σ* 2s: 2
- σ 2p_z: 2
- π 2p_x: 2
- π 2p_y: 2
- π* 2p_x: 0
- π* 2p_y: 0
- **Total in antibonding: 2 (σ*) + 2 (σ*) = 4 electrons**

3. **O2^- (17 electrons)**:
- Follows the same filling as O2 but with one additional electron in π* orbitals.
- π* 2p_x: 1
- π* 2p_y: 0
- **Total in antibonding: 2 (σ*) + 2 (σ*) + 1 (π*) = 5 electrons**

4. **O2-O2 (17 electrons)**:
- Similar to O2^- but with a different arrangement.
- **Total in antibonding: 2 (σ*) + 2 (σ*) + 1 (π*) = 5 electrons**

### Step 4: Compare the number of electrons in antibonding orbitals
- O2^2-: 8 electrons in antibonding orbitals
- O2: 4 electrons in antibonding orbitals
- O2^-: 5 electrons in antibonding orbitals
- O2-O2: 5 electrons in antibonding orbitals

### Conclusion
The species **O2^2-** contains the maximum number of electrons in the antibonding molecular orbitals, which is **8 electrons**.

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