Answer
See the detailed answer below.
Work Step by Step
$$\color{blue}{\bf [a]}$$
The given figure clearly shows that this is the ground state of nitrogen. The $p$ subshells have six states available, allowing them to comfortably accommodate three electrons without breaking the Pauli exclusion principle.
$$\color{blue}{\bf [b]}$$
This figure does not represent a possible electron configuration of an element since only two electrons are allowed in the $2s$ state.
$$\color{blue}{\bf [c]}$$
This figure does not represent a possible electron configuration of an element since the $2s$ states actually have lower energy compared to the $2p$ states. This means that in the ground state configuration, electrons fill the $2s$ orbital before they start populating the $2p$ orbital. This ordering is crucial because it dictates an atom's most stable arrangement of electrons.
