Q23 / 75 · JEE Main 2026 (02 April Shift 1) · Chemistry
One mole of an alkane (x) requires $8$ mole oxygen for complete combustion. Sum of number of carbon and hydrogen atoms in the alkane (x) is _______.
Correct answer: 17
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:
$C_n H_{2n+2} + \left(\dfrac{3n+1}{2}\right) O_2 \rightarrow n CO_2 + (n+1) H_2O$
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: $17$
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: $17$
Hence, the correct answer is 17.