In a hydrocarbon,the mass ratio of hydrogen and carbon is $1 : 3$. The empirical formula of the hydrocarbon is

In an analysis,the ratio of iodine to oxygen in a certain substance is $254:80$. What will be the formula of this substance? (Atomic mass $I = 127$,$O = 16$)

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

The simplest formula of a compound containing $50\%$ of element $X$ (at. wt. $= 10$) and $50\%$ of element $Y$ (at. wt. $= 20$) is

At $STP$,$2.8 \, L$ of a gaseous substance weighs $5.5 \, g$. If the compound contains $N$ and $O$ atoms,its molecular formula will be ..............

Chlorophyll,the green pigment in plants responsible for photosynthesis,contains $2.68\%$ of magnesium by mass. Calculate the number of magnesium atoms in $2.00 \ g$ of chlorophyll.