What is the percentage of carbon in urea (in $\%$)? $(At. mass C = 12, H = 1, N = 14, O = 16)$

An alkane has a $C/H$ ratio (by mass) of $5.1428$. Its molecular formula is

$0.765 \ g$ of an acid gives $0.535 \ g$ of $CO_2$ and $0.13 \ g$ of $H_2O$. The ratio of the percentage of $C$ and $H$ is:

Calculate the molecular formula of an iron oxide,in which the mass percentages of iron and oxygen are $69.9$ and $30.1$,respectively.

On complete combustion of $0.492 \ g$ of an organic compound containing $C, H$ and $O$,$0.7938 \ g$ of $CO_2$ and $0.4428 \ g$ of $H_2O$ were produced. The percentage composition of oxygen in the compound is $........$

Compound $A$ contains $8.7\,\%$ Hydrogen,$74\,\%$ Carbon and $17.3\,\%$ Nitrogen. The molecular formula of the compound is ....
Given : Atomic masses of $C$,$H$ and $N$ are $12$,$1$ and $14\, amu$ respectively.
The molar mass of the compound $A$ is $162\, g\, mol^{-1}$.