Question

Suppose that $A$ and $B$ form the compounds $B_{2} A_{3}$ and $B_{2} A$. If $0.05$ mole of $B_{2} A_{3}$ weighs $9\, g$ and $0.1$ mole of $B _{2} A$ weighs $10\, g$, the atomic weight of $A$ and $B$ respectively are

• A. 30 and 40
• B. 40 and 30
• C. 20 and 5
• D. 15 and 20

Answer 1

Answer: (B)

Let the atomic mass of $B=y g ; A=x g$
$\ln B _{2} A _{3}$
$2 y +3 x =$ mol. mass of $B _{2} A _{3}=\frac{\text { given weight }}{\text { mole }}$
$2 y+3 x=\frac{9}{0.05} g$
In $B _{2} A$
$\therefore 2 y +x=\frac{10}{0.1} g$
Solving $x$ and $y$
$\{ x=40\,\,\,y=30\}$