The percentage composition of carbon by mole in methane is ........... $ \% $

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 $= 120$).

$4 \ g$ of a hydrocarbon on complete combustion gave $12.571 \ g$ of $CO_2$ and $5.143 \ g$ of water. What is the empirical formula of the hydrocarbon?

In an analysis,the ratio of iodine to oxygen in a certain substance is $254:80$. What will be the formula of this substance? (Atomic mass $I = 127$,$O = 16$)

The molecular mass of an organic compound is $108 \ g \ mol^{-1}$. If $C, H,$ and $N$ atoms are present in the weight ratio of $9 : 1 : 3.5$,what is the molecular formula?

The value of $x$ in $KAl(SO_4)_x \cdot 12 H_2O$ is $.....$