The hybridizations of atomic orbitals of nitrogen in NO$$_2^ + $$, NO$$_3^ - $$ and NH$$_4^ + $$ respectively are
Explanation
X = $$1 \over 2$$ (VE + MA - c + a)
For $$NO^+_2$$, X = $$1 \over 2$$ (5 + 0 - 1) = 2, so sp hybridisation
For $$NO^-_3$$, X = $$1 \over 2$$ (5 + 0 + 1) = 3, so sp2 hybridisation
For $$NH^+_4$$, X = $$1 \over 2$$ (5 + 4 - 1) = 4, so sp3 hybridisation