The molecular formula of feldspar is

The percentage of $Se$ in peroxidase enzyme is $0.5\%$ by mass (atomic mass of $Se = 78.4 \ amu$). Then,the minimum molecular mass of enzyme which contains not more than one $Se$ atom is

Mass percentage of $C, H$ and $O$ in a compound are $60\%$,$13.33\%$ and $26.67\%$ respectively. The molecular weight of the compound is $60$. The molecular formula of the compound is

Substances $X$ and $Y$ have the same mass. If their atomic weights are $30$ and $20$ respectively,and the molecular weight of the compound is $120$,what is the molecular formula of the compound?

$A$ compound containing $Xe$ and $F$ has $63.8\%$ of $Xe$ by mass. Calculate the oxidation number of $Xe$ in this compound.

$A$ compound contains $75.8\%$ of $X$ and $24.2\%$ of $Y$ by mass. If the atomic weights of $X$ and $Y$ are $24$ and $16$ respectively,find the empirical formula of the compound.