The explanation for the presence of three unpaired electrons in the nitrogen atom can be given by which of the following?

Hund's rule

The correct answer is option 2. Hund's rule.

In chemistry, the electron configuration of an atom describes the distribution of its electrons among the various atomic orbitals. For nitrogen, the atomic number is 7, which means it has 7 electrons.

The electron configuration of nitrogen is $1s^2 2s^2 2p^3$. This notation indicates that there are 2 electrons in the 1s orbital, 2 electrons in the 2s orbital, and 3 electrons in the 2p orbital.

Now, the question pertains to the presence of three unpaired electrons in the nitrogen atom.

In atomic orbitals, electrons pair up with opposite spins (Pauli's exclusion principle), filling the orbitals from the lowest energy level to the highest (Aufbau principle). However, when filling degenerate orbitals (orbitals of the same energy level), Hund's rule comes into play.

Hund's rule states that electrons occupy separate orbitals within a subshell (in this case, the 2p subshell) before pairing up. This is because electrons repel each other due to their negative charge, and by occupying separate orbitals, they maximize the distance between them, thereby minimizing repulsion and lowering the overall energy of the atom.

So, in the case of nitrogen's 2p subshell, there are three available orbitals ($2p_x$, $2p_y$, and $2p_z$) with the same energy. According to Hund's rule, each of the three unpaired electrons occupies one of these three orbitals, each with the same spin. This arrangement maximizes the total spin (and thus the angular momentum) of the electrons, which results in a lower energy configuration compared to if the electrons were paired up in the same orbital. Therefore, three unpaired electrons are present in the nitrogen atom, consistent with Hund's rule.