What is the percentage of nitrogen in urea (in $\%$)?

An organic compound was found to contain $40.0 \% C$ and $6.66 \% H$. Find its molecular formula (molar mass $= 180$).

An organic compound has $42.1 \%$ carbon,$6.4 \%$ hydrogen and the remainder is oxygen. If its molecular weight is $342$,then its molecular formula is:

$A$ compound has the following composition by weight: $Na = 18.60 \%$,$S = 25.80 \%$,$H = 4.02 \%$,and $O = 51.58 \%$. Assuming that all the hydrogen atoms in the compound are part of water of crystallisation,the correct molecular formula of the compound is:

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

The empirical formula of a compound is $CH_2$. If the molar mass of the compound is $42 \ g/mol$,what is its molecular formula?