Mark the incorrect statement in the following .

Options

A. The bond order in the species `O_2, O_2^+` and `O_2^-` decreases as `O_2^(+) gt O_2 gt O_2^-`
B. The bond energy in a diatomic molecule always increases when an electron is lost
C. Electrons in antibonding MO contribute to repulsion between two atoms
D. With increase in bond order, bond length decreases and bond strength increases.

Explanation

To solve the question of identifying the incorrect statement among the given options, we will analyze each option step-by-step.

### Step 1: Analyze Option A
**Statement**: The bond order in the species O2, O2⁺, and O2⁻ decreases as O2⁺ > O2 > O2⁻.

1. **Determine the bond order for O2**:
- O2 has 16 electrons.
- The molecular orbital (MO) configuration is:
\[ \sigma_{1s}^2 \sigma_{1s}^*^2 \sigma_{2s}^2 \sigma_{2s}^*^2 \sigma_{2p_z}^2 \pi_{2p_x}^2 \pi_{2p_y}^2 \pi_{2p_x}^*^1 \pi_{2p_y}^*^1 \]
- Bond order = (Number of bonding electrons - Number of antibonding electrons) / 2
- Bond order for O2 = (10 - 6) / 2 = 2.

2. **Determine the bond order for O2⁺**:
- O2⁺ has one less electron than O2.
- Remove one electron from the antibonding orbitals:
- Bond order for O2⁺ = (10 - 5) / 2 = 2.5.

3. **Determine the bond order for O2⁻**:
- O2⁻ has one more electron than O2.
- Add one electron to the antibonding orbitals:
- Bond order for O2⁻ = (10 - 7) / 2 = 1.5.

4. **Conclusion for Option A**:
- The bond order increases as O2⁺ (2.5) > O2 (2) > O2⁻ (1.5).
- Thus, Option A is **correct**.

### Step 2: Analyze Option B
**Statement**: The bond energy in a diatomic molecule always increases when an electron is lost.

1. **Evaluate the statement**:
- This statement is too absolute with the word "always".
- For example, in the case of O2 to O2⁺, the bond order increases, and thus the bond energy increases.
- However, in the case of N2 to N2⁺, the bond order decreases, leading to a decrease in bond energy.

2. **Conclusion for Option B**:
- Since bond energy may either increase or decrease when an electron is lost, this statement is **incorrect**.

### Step 3: Analyze Option C
**Statement**: Electrons in antibonding MOs contribute to repulsion between two atoms.

1. **Evaluate the statement**:
- Electrons in antibonding molecular orbitals do indeed contribute to repulsion between the two atoms.
- This statement is **correct**.

### Step 4: Analyze Option D
**Statement**: With an increase in bond order, bond length decreases and bond energy increases.

1. **Evaluate the statement**:
- There is an inverse relationship between bond order and bond length (higher bond order = shorter bond length).
- Higher bond order also correlates with higher bond energy.
- This statement is **correct**.

### Final Conclusion
The incorrect statement among the options is **Option B**.