The hybridization of orbitals of N atom in $$NO_3^-$$, $$NO_2^+$$ and $$NH_4^+$$ are respectively :

Among the following the maximum covalent character is shown by the compound :

Which one of the following order represents the correct sequence of the increasing basic nature of the given oxides ?

A gas absorbs a photon of 355 nm and emits at two wavelengths. If one of the emissions is at 680 nm, the other is at :