JEE Main 2026 — Hydrocarbons Question with Solution

The general formula of an alkane is $C_n{H}_{2n+2}$.

The balanced chemical equation for the complete combustion of an alkane is:

$C_n{H}_{2n+2}+\left(\frac{3n+1}{2}\right)O_2\to nC{O}_2+(n+1)H_{2}O$

Given that $1$ mole of the alkane requires $8$ moles of oxygen for complete combustion, we equate the stoichiometric coefficient of $O_2$ to $8$:

$\frac{3n+1}{2}=8$

$3n+1=16$

$3n=15$

$n=5$

The molecular formula of the alkane is $C_5{H}_{12}$.

The number of carbon atoms is $5$ and the number of hydrogen atoms is $12$.

Sum of the number of carbon and hydrogen atoms $=5+12=17$.

Answer: $17$