Question

A trivalent metal oxide contains $30\%$oxygen. Find the gram atomic mass of the metal present in the oxide.

• A. $72g$
• B. $160g$
• C. $112g$
• D. $56g$

Answer 1

The correct option is D

$56g$

Explanation of correct option:

• The formula of a trivalent metal oxide is ${\mathrm{M}}_2{\mathrm{O}}_3$.
• The mass of oxygen in this oxide is $3\times 16g=48g.$
• According to the question, $30\%$mass of the metal oxide is oxygen. Therefore, $30\%=48g\Rightarrow 70\%=\frac{48\times 70}{30}=112g.$
• Thus, the mass of metal present in the trivalent metal oxide$\left({\mathrm{M}}_2{\mathrm{O}}_3\right)$ is $112g.$
• Therefore, the gram atomic mass of the metal in the metal oxide is $\frac{112g}{2}=56g.$

Hence, the correct option is (D).