What is the difference between $NO_2$ and $NO_2^-$? Explain.

(N/A) The total number of valence electrons in $NO_2$ is $5 + (2 \times 6) = 17$.
The total number of valence electrons in $NO_2^-$ is $5 + (2 \times 6) + 1 = 18$.
Since $NO_2$ has an odd number of electrons $(17)$,it violates the octet rule (it is a free radical),whereas $NO_2^-$ has an even number of electrons $(18)$ and follows the octet rule for the central nitrogen atom.