The cyanide ion, $CN^{-}$ and $N_2$ are isoelectronic . But in contrast to $CN^{-},N_2$ is chemically inert, because of

Question

$(a)\;\text{$\pi$ bonding} \\ (b)\;\text{absence of bond polarity} \\(c)\;\text{unsymmetrical electron distribution } \\(d)\;\text{Presence of more number of electrons in bonding orbitals}$