If $N_A$ is the Avogadro's number then number of valence electrons in 4.2g of nitride ion($N^{3-})$ is

Question

$\begin{array}{1 1}(a)\;2.4N_A&(b)\;4.2N_A \\(c)\;1.6N_A&(d)\;3.2N_A\end{array} $