One mole of alkane reacts with 8 mole of O₂. The molecular formula of alkane is

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The correct option is $C_5{H}_{12}$.

To find the molecular formula of the alkane, we can write down the general balanced chemical equation for the complete combustion of an alkane.

The general formula for an alkane is $C_n{H}_{2n+2}$, where n is the number of carbon atoms.

The balanced equation for the combustion of one mole of this alkane with oxygen ($O_2$) to form carbon dioxide ($C{O}_2$) and water ($H_{2}O$) is:
$C_n{H}_{2n+2}+\left(\frac{3n+1}{2}\right)O_2\to nC{O}_2+(n+1)H_{2}O$

According to the given problem, 1 mole of the alkane reacts with 8 moles of $O_2$. Therefore, the stoichiometric coefficient of $O_2$ in the balanced equation must be equal to 8:
$\frac{3n+1}{2}=8$

Now, we solve for n:
$3n+1=16$
$3n=15$
$n=5$

Substituting n = 5 into the general formula of the alkane ($C_n{H}_{2n+2}$):
Number of carbon atoms (C) = 5
Number of hydrogen atoms (H) = 2(5) + 2 = 12

Thus, the molecular formula of the alkane is $C_5{H}_{12}$ (pentane).