The percentage of $N_2$ in urea is about

Caffeine has a molecular weight of $194$. If it contains $28.9\%$ by mass of nitrogen,the number of atoms of nitrogen in one molecule of caffeine is:

On analysis,a certain compound was found to contain iodine and oxygen in the ratio of $254 \ g$ of iodine and $80 \ g$ of oxygen. The atomic mass of iodine is $127$ and that of oxygen is $16$. Which of the following is the formula of the compound?

Define empirical formula and molecular formula.

By combustion of $0.2475 \ g$ of an organic compound,$0.4950 \ g$ of $CO_2$ and $0.2025 \ g$ of $H_2O$ are obtained. Calculate the percentage of $C, H,$ and $O$. Given atomic masses: $C = 12, H = 1, O = 16$.

Which compound has the highest percentage of hydrogen by mass?