Which of the following species have maximum number of unpaired electrons ?

Options

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

Explanation

To determine which of the given species has the maximum number of unpaired electrons, we will analyze each species according to molecular orbital theory. Let's go through the steps one by one.

### Step 1: Determine the number of electrons in each species.
- **O2+**: This species has 15 electrons.
- **O2**: This species has 16 electrons.
- **O2-**: This species has 17 electrons.
- **O2 2-**: This species has 18 electrons.

### Step 2: Fill the molecular orbitals for O2+ (15 electrons).
1. The molecular orbital filling order is: σ(1s), σ*(1s), σ(2s), σ*(2s), σ(2p), π(2p), π*(2p).
2. Fill the orbitals:
- σ(1s): 2 electrons
- σ*(1s): 2 electrons
- σ(2s): 2 electrons
- σ*(2s): 2 electrons
- σ(2p): 2 electrons
- π(2p): 2 electrons
- π*(2p): 1 electron (unpaired)

Total: 2 + 2 + 2 + 2 + 2 + 2 + 1 = 15 electrons.

**Unpaired Electrons in O2+: 1**

### Step 3: Fill the molecular orbitals for O2 (16 electrons).
1. Following the same filling order:
- σ(1s): 2 electrons
- σ*(1s): 2 electrons
- σ(2s): 2 electrons
- σ*(2s): 2 electrons
- σ(2p): 2 electrons
- π(2p): 2 electrons
- π*(2p): 2 electrons (both orbitals half-filled)

Total: 2 + 2 + 2 + 2 + 2 + 2 + 2 = 16 electrons.

**Unpaired Electrons in O2: 2**

### Step 4: Fill the molecular orbitals for O2- (17 electrons).
1. Following the same filling order:
- σ(1s): 2 electrons
- σ*(1s): 2 electrons
- σ(2s): 2 electrons
- σ*(2s): 2 electrons
- σ(2p): 2 electrons
- π(2p): 2 electrons
- π*(2p): 3 electrons (one unpaired in π*(2p))

Total: 2 + 2 + 2 + 2 + 2 + 2 + 3 = 17 electrons.

**Unpaired Electrons in O2-: 1**

### Step 5: Fill the molecular orbitals for O2 2- (18 electrons).
1. Following the same filling order:
- σ(1s): 2 electrons
- σ*(1s): 2 electrons
- σ(2s): 2 electrons
- σ*(2s): 2 electrons
- σ(2p): 2 electrons
- π(2p): 2 electrons
- π*(2p): 2 electrons (all orbitals fully filled)

Total: 2 + 2 + 2 + 2 + 2 + 2 + 2 = 18 electrons.

**Unpaired Electrons in O2 2-: 0**

### Step 6: Compare the number of unpaired electrons.
- O2+: 1 unpaired electron
- O2: 2 unpaired electrons
- O2-: 1 unpaired electron
- O2 2-: 0 unpaired electrons

### Conclusion:
The species with the maximum number of unpaired electrons is **O2**, which has **2 unpaired electrons**.