Question

What is the reason of presence of three unpaired electrons in $$\mathrm{N}$$ atom?

Answer 1

The atomic number of Nitrogen is $$7$$ and its electronic configuration is $$1s^{2}, 2s^{2}, 2p^{3}$$
Arrangement of electrons in a sub-shell of an atom is given by Hund's rule which states that pairing of the electron in the orbitals of the same sub-shell will not take place until all the orbitals are singly filled.

Thus, according to the rule, the pairing of electrons in orbitals of $$2p$$ does not start in $$N$$ because out of $$5$$ electrons, $$2$$ electrons go to $$2s$$ and $$3$$ electrons are singly occupied in $$2p$$ sub-shell.

Thus, there are $$3$$ unpaired electrons in Nitrogen.