The empirical formula of a compound is $CH_2O$ and its molecular mass is $90$. The molecular formula of the compound is:

An oxide of iron contains $69.9\%$ iron. Its empirical formula is: (Given: Molar mass of $Fe$ and $O$ are $56$ and $16 \text{ g mol}^{-1}$ respectively.)

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?

An organic compound contains carbon,hydrogen,and oxygen with percentages of $38.71\%$,$9.67\%$,and $51.62\%$ respectively. Determine the empirical formula of this compound.

One compound contains $4.07\%$ Hydrogen,$24.47\%$ Carbon and $71.65\%$ Chlorine. Its molar mass is $98.96\ g/mol$. Find the empirical formula and molecular formula.

In a compound made of $X$ and $Y$,their masses are equal. If the atomic masses of $X$ and $Y$ are $30$ and $20$ respectively,then the molecular formula of the compound will be ......... (Its molecular mass $= 120$).