Answer
$NH_3$ is a Lewis base.
Work Step by Step
- $N$ has, naturally, 5 electrons in its valence shell, and it is making 3 covalent bonds with the hydrogens. Which means that, it has 8 electrons in its valence shell, and 2 of them are not being used (lone pair).
- Since the central atom, $N$, has a lone pair that can be donated, $NH_3$ is a Lewis base.
