If 12 g of alkaline earth metal gives 14.8 g of its nitride, then what is the atomic weight of metal?

The correct option is C 40

Let the metal be M with atomic wt. be $x$.

So, $3M+N_2\to M_3{N}_2$

$3x$
$3x+28$

So, $\frac{12}{3x}=\frac{14.8}{(3x+28)}$

Which in solving for $x$ gives 40.

The metal is calcium and its nitride is $C{a}_3{N}_2$.