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?

$116 \ g$ of a substance upon dissociation reaction,yields $7.5 \ g$ of hydrogen,$60 \ g$ of oxygen and $48.5 \ g$ of carbon. Given that the atomic masses of $H, O$ and $C$ are $1, 16$ and $12$ respectively. The data agrees with how many formulae of the following?
$(A)$ $CH_3COOH$
$(B)$ $HCHO$
$(C)$ $CH_3OOCH_3$
$(D)$ $CH_3CHO$

$A$ hydrocarbon contains $85.7 \% C$. If $42 \, mg$ of the compound contains $3.01 \times 10^{20}$ molecules,the molecular formula of the compound will be

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 molar mass of caffeine is $194$. It contains $28.9\%$ of nitrogen by mass. The number of nitrogen atoms in one molecule of caffeine is:

The molecular formula of potash alum is