In $\mathrm{NO}_3^{-}$ion, number of the bond pair and the lone pair of electrons on nitrogen atom are:

Nitrogen forms a coordinate bond with Oxygen as it cannot have 5 bonds. Although 2 electrons are shared in a coordinate bond, the number of bond pairs is taken to be 1. Hence the number of bond pairs are 4 and the number of lone pairs is 0 .
The valence shell electron pair repulsion (VSEPR) model relies on the idea that electron pairs repel each other. This causes bonding and lone pair electrons to stay as far away from each other as possible. The electron pair repulsion gives rise to geometry of the molecules and compounds.