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 ...............

Two elements,$X$ and $Y$,have atomic numbers $33$ and $17$,respectively. The molecular formula of a stable compound formed between them is

In which of the following pairs of compounds is the ratio of $C$,$H$,and $O$ the same?

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 $g \ mol^{-1}$; $O=16, Mg=24, P=31$)

$A$ $1000 \ g$ sample of $NaOH$ contains $3 \ moles$ of $O$ atoms. What is the $Purity$ of $NaOH$ $\dots \dots \dots \dots \dots \dots \%$

An organic compound has been found to possess the empirical formula $CH_2O$ and molecular weight $90$. The molecular formula of it is $(C = 12, H = 1, O = 16)$.