In the combustion reaction of alkanes, if 1 mole of ethane is...

The general equation for the combustion of an alkane $C_nH_{2n+2}$ is given by:

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

For ethane ($C_2H_6$), $n = 2$.

Substituting $n = 2$ in the coefficient of $O_2$:

Moles of $O_2$ required $= \dfrac{3(2)+1}{2} = \dfrac{7}{2} = 3.5$

The balanced chemical equation is:

$C_2H_6 + 3.5 O_2 \rightarrow 2 CO_2 + 3 H_2O$

Thus, $1$ mole of ethane requires $3.5$ moles of oxygen.

Answer: $3.5$