The formula used to calculate the bond order is

Options

A. `BO=1/2[N_b-N_a]`
B. `BO=1/2[N_a-N_b]`
C. `BO=N_b-N_a`
D. `BO=1/3[N_b-N_a]`

Answer

To calculate the bond order of a molecule, we can use the following formula:

### Step-by-Step Solution:

1. **Understanding Bond Order**:
Bond order is a measure of the number of chemical bonds between a pair of atoms. It can be calculated using the formula that takes into account both bonding and anti-bonding electrons.

2. **The Formula**:
The formula for calculating bond order is:
\[ \text{Bond Order} = \frac{1}{2} \times (N_b - N_a) \]
where:
- \(N_b\) = Number of bonding electrons
- \(N_a\) = Number of anti-bonding electrons

3. **Example Calculation**:
Let's consider the molecule \(Li_2\) as an example to illustrate how to use this formula.
- First, we write the electronic configuration of \(Li_2\):
- \(1s \sigma^2\) (2 electrons in bonding)
- \(1s \sigma^* (0)\) (0 electrons in anti-bonding)
- Here, we have:
- \(N_b = 2\) (bonding electrons)
- \(N_a = 0\) (anti-bonding electrons)

4. **Substituting Values into the Formula**:
\[ \text{Bond Order} = \frac{1}{2} \times (2 - 0) = \frac{1}{2} \times 2 = 1 \]
Thus, the bond order for \(Li_2\) is 1.

5. **Conclusion**:
The correct formula to calculate bond order is:
\[ \text{Bond Order} = \frac{1}{2} \times (N_b - N_a) \]