c
\(N\) forms \(NCl_3,\, N_2O_5\) and \(Ca_3N_2\). Nitrogen, due to absence of empty \(d-\) orbitals, cannot extend its covalency by more than three and hence do not form \(NCl_5\). Due to its small size and high electronegativity it can accept \(3\) electrons to form \(N^{3-}\) ion (\(Ca_3N_2\))