Question

$3$ atoms of metal $M$ combine with $2$ atoms of nitrogen to give a compound containing $28 \%$ nitrogen and $72 \%$ of metal. What is the atomic weight of metal?

• A. 36
• B. 24
• C. 12
• D. 48

Answer 1

Answer: (B)

Formula of the compound must be $M_{3} N _{2}$

In $100 \,g$ compound, $28\, g$ nitrogen combines with $72 \,g$ metal.

i.e. $72=3 \times$ atomic mass of metal

$\therefore $ Atomic mass of metal $=72 / 3=24$

Alternatively, $\frac{28}{14}: \frac{72}{x}:: 2: 3$ (Say atomic mass of metal $\left.=x\right)$

$\frac{72}{x} \times 2=\frac{28}{14} \times 3 \Rightarrow x=\frac{72 \times 2}{6}=24$