An organic compound made of $C$, $H$ and $N$ contains $20 \%$ nitrogen. Its molecular weight is:

$A$ sample of a hydrate of barium chloride weighing $61 \ g$ was heated until all the water of hydration was removed. The dried sample weight is $52 \ g$. The formula of the hydrated salt is: (atomic mass: $Ba = 137 \ amu, Cl = 35.5 \ amu$)

$A$ compound contains $8\%$ sulfur by weight. The minimum molecular weight of the compound is:

$25 \ g$ of an unknown hydrocarbon upon burning produces $88 \ g$ of $CO_2$ and $9 \ g$ of $H_2O$. This unknown hydrocarbon contains:

Insulin contains $3.4\%$ sulfur. What is the minimum molecular weight of insulin?

How much copper can be obtained from $100 \, g$ of copper sulphate $(CuSO_{4})$?