What coefficients are required to balance the following equation?
$N_2+H_2\to {NH}_3$

The correct option is C $1,3,2$
$H$ are in the ratio of $2:3$ before reaction. Make it balance by writing $3$ before $H_2$ and $2$ before $N{H}_3$. $N$ is $2$ in number, now, both side. So, total reaction is balanced. $N_2+3H_2⟶2N{H}_3.$