What is the percentage of nitrogen in urea (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 $I = 127$,$O = 16$)

One compound contains $4.07\%$ Hydrogen,$24.47\%$ Carbon and $71.65\%$ Chlorine. Its molar mass is $98.96\ g/mol$. Find the empirical formula and molecular formula.

Analysis of an organic compound shows $C = 40\%$,$H = 13.33\%$,and $N = 46.67\%$. Its empirical formula is ....

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?

$A$ compound $X$ contains $32 \%$ of $A$,$20 \%$ of $B$,and the remaining percentage of $C$. Then,the empirical formula of $X$ is:
(Given atomic masses of $A = 64$,$B = 40$,$C = 32 \ u$)