Question

Which of the following statements is not correct from the view point of molecular orbital theory?

• A. $Be_2$ is not a stable molecule.
• B. $He_2$ is not stable but $He_2$ is expected to exist.
• C. Bond strength of $N_2$ is maximum amongst the homonuclear diatomic molecules belonging to the second period.
• D. The order of energies of molecular orbitals in $\mathrm{N}_{2}$ molecule is $\sigma 2 s<\sigma^{*} 2 s<\sigma 2 p_{z}<\left(\pi 2 p_{x}=\pi 2 p_{y}\right)<\left(\pi^{*} 2 p_{x}\right.$ $\left.=\pi^{*} 2 p_{y}\right)<\sigma^{*} 2 p_{z}$

Answer 1

Answer: (D)

For $\mathrm{N}_{2}, \sigma 2 p_{z}$ has higher energy than $\pi 2 p_{x}$ and $\pi 2 p_{y}$ hence, the correct order will be
$ \sigma2s, \sigma^{*} 2 s, \pi 2 p_{x}=\pi 2 p_{y}, \sigma 2 p_{z}, \pi^{*} 2 p_{x}=\pi^{*} 2 p_{y}, \sigma^{\star} 2 p_{z}$