Chemistry - Complete P-block Question with Solution | TestHub

Based on the given characteristics (paramagnetic diatomic gas with two unpaired electrons), the gas r(g) is identified as Oxygen (O₂).

The molecular orbital (MO) configuration of O₂ (16 electrons) is:

$${\sigma }_{1s}{}^2{\sigma }_{1s}^{\ast 2}{\sigma }_{2s}{}^2{\sigma }_{2s}^{\ast 2}{\sigma }_{2p_z}{}^2{\pi }_{2p_x}{}^2={\pi }_{2p_y}{}^2{\pi }_{2p_x}^{\ast 1}={\pi }_{2p_y}^{\ast 1}$$

In homonuclear diatomic molecules, all $\sigma$-bonding molecular orbitals (BMOs) have inversion symmetry and are classified as gerade (e.g., ${\sigma }_{1s}$, ${\sigma }_{2s}$, ${\sigma }_{2p_z}$), whereas $\pi$-bonding molecular orbitals are ungerade.

The occupied gerade BMOs present here are ${\sigma }_{1s}$, ${\sigma }_{2s}$, and ${\sigma }_{2p_z}$. Therefore, the total number of occupied gerade BMOs is 3 (Option B).