Question

Elements $A$ and $B$ form two compounds $B_2{A}_3$ and $B_{2}A$. $0.05$ moles of $B_2{A}_3$ weight $9.0g$ and $0.10$ mole of $B_{2}A$ weight $10g$ atomic weight of $A$ and $B$ are:

• A. $20$ and $30$
• B. $30$ and $40$
• C. $40$ and $30$
• D. $30$ and $20$

Answer 1

Answer: (C)

$40$ and $30$

Molar mass of $B_2{A}_3=\frac{9}{0.05}=\frac{900}{5}$

$\Rightarrow 2B+3A=180$

Molar mass of $B_{2}A=\frac{10}{0.1}=100$

$\Rightarrow 2B+A=100$

Solving eq$\left(1\right)$ and $\left(2\right)$

$\begin{array}{c}2A=80\\ A=40\\ B=30\end{array}$

Hence, the correct option is $C$