How much copper can be obtained from $100 \ g$ of copper sulfate $(CuSO_4)$ (in $g$)?

In a substance,the number of atoms of $Cr$ and $O$ are $4.8 \times 10^{10}$ and $9.6 \times 10^{10}$ respectively. The empirical formula of the substance is .......

Determine the molecular formula of an oxide of iron in which the mass per cent of iron and oxygen are $69.9$ and $30.1$ respectively. Given that the molar mass of the oxide is $159.69 \, g \, mol^{-1}$.

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

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

$A$ substance contains $38.8\% \ C$,$16.0\% \ H$,and $45.2\% \ N$. What is the empirical formula of the substance?