One mole of an alkane (x) requires 8 mole oxygen for complete...

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

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

$C_n H_{2n+2} + \left(\dfrac{3n+1}{2}\right) O_2 \rightarrow n CO_2 + (n+1) H_2O$

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

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

$3n + 1 = 16$

$3n = 15$

$n = 5$

The molecular formula of the alkane is $C_5H_{12}$.

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: $17$