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

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

$A$ compound contains $75.8\%$ of $X$ and $24.2\%$ of $Y$ by mass. If the atomic weights of $X$ and $Y$ are $24$ and $16$ respectively,find the empirical formula of the compound.

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?

$A$ substance contains $38.8\%$ carbon,$16\%$ hydrogen,and $45.2\%$ nitrogen. What is the empirical formula of this substance?

$120 \ g$ of an organic compound that contains only carbon and hydrogen gives $330 \ g$ of $CO_{2}$ and $270 \ g$ of water on complete combustion. The percentage of carbon and hydrogen,respectively,are ...... .