Question

$12$ gm of an alkaline earth metal gives $14.8$g of its nitride. The atomic mass of metal is:

• A. $12$
• B. $24$
• C. $20$
• D. $40$

Answer 1

Answer: (D)

$40$

Let the alkaline earth metal be $A$.

$\therefore 3A+N_2\to A_3{N}_2$

$\Rightarrow \frac{Molecularmassofcompound}{Atomicmassofmetal}$

$=\frac{Wt.ofcompound}{Wt.ofmetal}$

Let the atomic mass of metal be $x$.

$\to$ Molecular mass of compound$=3x+28$

$\Rightarrow \frac{3x+28}{3x}=\frac{14.8}{12}$

$\Rightarrow x=40$