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

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

Both $CN^{-}$ and $N_2$ molecules have the same $MO$ diagrams but differ only in bond polarity.
$CN^{-}$ ion is reactive due to presence of bond polarity.
While $N_2$ is inert due to absence of bond polarity.
Hence b is the correct answer.