Calculate the percentage composition of element $P$ in ${H_3PO_4}$. (in $\%$)

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 $I = 127$,$O = 16$)

An organic compound contains $C = 38.8\%$,$H = 16\%$ and $N = 45.2\%$. The empirical formula of the compound is:

What is the mass percentage of carbon in urea (in $\%$)? (molar mass of urea $= 60 \ g \ mol^{-1}$)

If a compound contains $C = 18.5\%$,$H = 1.55\%$,$Cl = 55.04\%$,and $O = 24.81\%$,then its empirical formula is .....

In a compound made of $X$ and $Y$,their masses are equal. If the atomic masses of $X$ and $Y$ are $30$ and $20$ respectively,then the molecular formula of the compound will be ......... (Its molecular mass $= 120$).