Question

Which of the following molecule has zero bond order?

• A. $\mathrm{O_2}$
• B. $\mathrm{He_2}$
• C. $\mathrm{N_2}$
• D. $\mathrm{H_2}$

Hint:

A molecule with zero bond order is unstable and cannot exist under normal conditions.

Answer 1

The Correct Option is B

Step 1: Recall the bond order formula.
\[ \text{Bond order} = \dfrac{N_b - N_a}{2} \]
where \(N_b\) = number of bonding electrons and \(N_a\) = number of antibonding electrons.
Step 2: Analyze the molecule \(\mathrm{He_2}\).
Each helium atom has 2 electrons, so total electrons = 4.
Electronic configuration: \(\sigma_{1s}^2 \, \sigma_{1s}^{*2}\)
Step 3: Calculate bond order.
\[ \text{Bond order} = \dfrac{2 - 2}{2} = 0 \]
Step 4: Conclusion.
Since bond order is zero, \(\mathrm{He_2}\) does not exist as a stable molecule.