The hybridizations of atomic orbitals of nitrogen
in ``NO_2^+``, ``NO_3^-``and ``NH_4^+`` respectively are
(1) ``sp, sp^2 and sp^3``
(2) ``sp^2, sp and sp^3``
(3) ``sp, sp^3 and sp^``2
(4) ``sp^2, sp^3 and sp``