A nitrogen atom needs to gain three electrons to achieve a noble gas configuration.

Here's why:

* Nitrogen's electron configuration: Nitrogen has 7 electrons, with the configuration 1s² 2s² 2p³.

* Noble gas configuration: The nearest noble gas to nitrogen is Neon (Ne), which has 10 electrons (1s² 2s² 2p⁶).

* Gaining electrons: Nitrogen needs to gain three more electrons to fill its 2p orbital and achieve the same electron configuration as Neon.

This is why nitrogen typically forms anions with a -3 charge (N³⁻).