How many grams of oxygen are present in $32.2 \ g$ of $Na_2SO_4 \cdot 10H_2O$ (in $g$)?

The percentage of $Se$ in peroxidase anhydrous enzyme is $0.5\%$ by weight (atomic weight $= 78.4$). Then,the minimum molecular weight of peroxidase anhydrous enzyme is:

Which of the following has the highest chlorine content by mass?

If we want to study the relative arrangement of atoms in a molecule,we study:

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 $159.69 \, g \, mol^{-1}$.

$0.5 \ g$ of an organic compound on combustion gave $1.46 \ g$ of $CO_2$ and $0.9 \ g$ of $H_2O$. The percentage of carbon in the compound is $...........$ ($NEAREST$ $INTEGER$). [$GIVEN$: Molar mass in $g \ mol^{-1}$: $C: 12, H: 1, O: 16$]