The molecular mass of caffeine is $194 \, a.m.u.$. It contains $28.9 \%$ of nitrogen by mass. The number of nitrogen atoms in one molecule of caffeine is ...............

$A$ metal oxide $M$ contains $40\%$ oxygen by mass. The atomic mass of metal $M$ is $24$. The empirical formula of the oxide is....

The formula of ferric sulphate is:

Two oxides of a metal contain $50\%$ and $40\%$ of the metal,respectively. The formula of the first oxide is $MO$. What is the formula of the second oxide?

Find the empirical formula of an organic compound if it contains $18.6 \% C$,$1.55 \% H$,and $55.04 \% Cl$. (Atomic masses: $C=12$,$H=1$,$Cl=35.5$,$O=16$)

By usual analysis,$1.00 \ g$ of compound $(X)$ gave $1.79 \ g$ of magnesium pyrophosphate. The percentage of phosphorus in compound $(X)$ is: (nearest integer)
(Given,molar mass in $g \ mol^{-1}$; $O=16, Mg=24, P=31$)