Some Basic Concepts of Chemistry

Given,

$\%$ of element $(M)=68 \%$

and of oxygen $(\mathrm{O})=32 \%$

Atomic mass of $M=34$

Thus, empirical formula of $M_x \mathrm{O}_y$ is

element $\longrightarrow \%$ of mass $\longrightarrow$ moles $(n)$

$\begin{aligned} & M \longrightarrow 68 \longrightarrow 68 / 34=2 \\ & \mathrm{O} \longrightarrow 32 \longrightarrow 32 / 16=2 \end{aligned}$

Hence, empirical forumula of given compound is $\mathrm{M}_2 \mathrm{O}_2$ or $M \mathrm{O}$.

Thus, option (a) is the correct.