Question

Which contains at least one $ {e^ - } $ in $ \sigma 2p $ bonding MO:
(A) $ {O_2} $
(B) $ {B_2} $
(C) $ {C_2} $
() $ L{i_2} $

Answer 1

Hint :This question is based on the widely used concept of representation of electronic configuration with the help of molecular orbitals. This is an advanced representation of electronic configuration and it has cleared a lot of dilemmas regarding the presence of various exceptional cases in the context of relation between electronic configuration and the properties of the element.

Complete Step By Step Answer:
The valence-bond theory failed to adequately explain how certain compounds, such as resonance-stabilized compounds, contain two or more analogous bonds whose bond orders lie between those of a single bond and those of a double bond. The molecular orbital theory was shown to be more powerful than the valence-bond hypothesis in this case (since the orbitals described by the MOT reflect the geometries of the molecules to which it is applied).
The molecular orbital theory states, in simple terms, that each atom tends to join and form molecular orbitals. Electrons are found in distinct atomic orbitals as a result of this arrangement, and they are frequently connected with different nuclei. In a molecule, an electron can be found anywhere in the molecule.
In the above question, $ {O_2} $ has 16 electrons, which can be arranged in a certain manner in atomic orbitals:
 $ {O_2} = {(\sigma 1s)^2}{({\sigma ^*}1s)^2}{(\sigma 2s)^2}{({\sigma ^*}2s)^2}{(\sigma 2{p_z})^2}(\pi 2{p_x}^2 = \pi 2{p_y}^2)({\pi ^*}2{p_x}^1 = {\pi ^*}2{p_y}^1) $
So, it can clearly be observed that it has more than one electron in $ \sigma 2p $ orbital.
So, the correct answer is (A).

Note :
One of the most significant effects of the molecular orbital theory after its formulation was that it opened up new avenues for understanding the bonding process. According to this idea, molecule orbitals are essentially linear combinations of atomic orbitals. The Schrödinger equation is further approximated using the Hartree–Fock (HF) or density functional theory (DFT) models.