What is the mass percent of oxygen in ethanol $(C_2H_5OH)$ (in $\%$)?

Quantitative analysis of an organic compound $(X)$ shows the following percentage composition: $C: 14.5\%$,$Cl: 64.46\%$,and $H: 1.8\%$. The empirical formula mass of the compound $(X)$ is $.......... \times 10^{-1}$. (Given molar mass in $g \ mol^{-1}$ of $C: 12, H: 1, O: 16, Cl: 35.5$)

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

Nickel steel contains $3-5 \%$ of $Ni$. (in $-5 \%$)

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

An organic compound made of $C$, $H$ and $N$ contains $20 \%$ nitrogen. Its molecular weight is: