Question

A compound $X_2{O}_3$ contains $31.58\%$ oxygen by weight. The atomic mass of $X$ is _________.

• A. $34.66gmo{l}^{-1}$
• B. $45.01gmo{l}^{-1}$
• C. $52.00gmo{l}^{-1}$
• D. $104.00gmo{l}^{-1}$

Answer 1

Answer: (C)

$52.00gmo{l}^{-1}$

In $X_2{O}_3$,

Percentage of oxygen by weight = $31.58$

Percentage of X by weight = $68.42$

Let the atomic weight of X = x

$\frac{2x}{2x+48}\times 100$ = $68.42$

$\therefore$ $x$ = $51.99$

So, atomic mass of X is $52gmo{l}^{-1}$