Calculate the molecular formula of an iron oxide,in which the mass percentages of iron and oxygen are $69.9$ and $30.1$,respectively.

The mass $\%$ of carbon in $C_{57}H_{110}O_6$ is

$A$ gas is found to have a formula $[CO]_x$. If its vapour density is $70$,the value of $x$ is

Among the following,the compound with the highest percentage of chlorine is:

$2.0 \text{ g}$ of a bromo hydrocarbon $(X)$ was subjected to Carius analysis,which gave $3.36 \text{ g}$ of $AgBr$. The percentage of carbon in the compound $(X)$ is $26.7\%$. The total number of carbon atoms in the empirical formula for compound $(X)$ is . . . . . . .

If the weight percentage of $Se$ (at. wt. $78.4$) in peroxidase anhydrous enzyme is $0.5 \%$,what is the minimum molecular weight of the enzyme?