b
If an atom has lone pairs and bonded electron pairs, the greater lone pair-lone pair repulsions will cause bond angle to decrease between bonded atoms.

\(NH _2^{-}\) has \(2\) bond pairs and \(2\) lone pairs of electrons.

\(NH _3\) has \(3\) bond pairs and \(1\) lone pair.

\(NH _4^{-}\) has \(4\) bond pairs.

Bond pair - Bond pair electron repulsions \(\,<\,\) Bond pair - Lone pair electron

repulsions \(\,<\,\) Lone pair - Lone pair electron repulsions

Greater lone pair - lone pair repulsions among electrons causes the \(H - N - H\)

bond angle to decrease. This effect is greatest for \(NH _2^{-}\), followed by \(NH _3\).

Hence, the correct order is: \(NH _4^{+}\,>\, NH _3\,>\, NH _2^{-}\)