$CO$ contains $14$ electrons ( $6$ from carbon and $8$ from oxygen).

$NO ^{-}$contains $16$ electrons ( $7$ from nitrogen, $8$ from oxygen, add $1$ more for negative charge).

$NO ^{+}$has $14$ electrons ( $7$ from nitrogen, $8$ from oxygen, subtract $1$ for positive charge).

$CN ^{-1}$ has $14$ electrons ( $7$ from nitrogen, $6$ from carbon, add $1$ more for negative charge).

$N _2$ has $14$ electrons ( $7$ from nitrogen each).

The species containing the same number of electrons have the same bond order.

So $NO ^{-}$is the only one which has bond order different. So option $A$ is correct.