Which of the following substances produces $17.6 \ g$ of $CO_2$ and $7.2 \ g$ of $H_2O$ upon complete combustion with excess oxygen?

$A$ welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives $3.38 \ g$ of carbon dioxide,$0.690 \ g$ of water and no other products. $A$ volume of $10.0 \ L$ of this welding gas (measured at $STP$) is found to weigh $11.6 \ g$. Calculate: $(i)$ Empirical formula,$(ii)$ Molar mass of the gas,$(iii)$ Molecular formula.

$60 \ g$ of a compound on analysis gave $C = 24 \ g$,$H = 4 \ g$ and $O = 32 \ g$. Its empirical formula is

Mass percentage of $C, H$ and $O$ in a compound are $60\%$,$13.33\%$ and $26.67\%$ respectively. The molecular weight of the compound is $60$. The molecular formula of the compound is

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 $........$

The percentage of $N_2$ in urea is about