Answer: Option 12.5 is the correct answer.
Explanation:
The given reaction is as follows.
![C_{8}H_{18} + x(O_{2} + 3.76N_{2}) \rightarrow Products](https://tex.z-dn.net/?f=C_%7B8%7DH_%7B18%7D%20%2B%20x%28O_%7B2%7D%20%2B%203.76N_%7B2%7D%29%20%5Crightarrow%20Products)
As it is a combustion reaction so, nitrogen will not take part in it and hence, it will remain the same on both sides of the reaction.
Also, it is known that in a combustion reaction oxygen reacts with a hydrocarbon and results in the formation of carbon dioxide and water. Therefore, for the above reaction we write the complete reaction equation as follows.
![C_{8}H_{18} + x(O_{2} + 3.76N_{2}) \rightarrow CO_{2} + H_{2}O + 3.76 N_{2}](https://tex.z-dn.net/?f=C_%7B8%7DH_%7B18%7D%20%2B%20x%28O_%7B2%7D%20%2B%203.76N_%7B2%7D%29%20%5Crightarrow%20CO_%7B2%7D%20%2B%20H_%7B2%7DO%20%2B%203.76%20N_%7B2%7D)
or,
as nitrogen is not taking part in the reaction.
Number of atoms on reactant side are as follows.
C = 8
H = 18
O = 2
Number of atoms on product side are as follows.
C = 1
O = 3
H = 2
Therefore, to balance this equation we multiply oxygen on reactant side by 12.5. Also, we multiply carbondioxide by 8 and water by 9 on product side. Hence, the complete balanced chemical equation is as follows.
![C_{8}H_{18} + 12.5O_{2} \rightarrow 8CO_{2} + 9H_{2}O](https://tex.z-dn.net/?f=C_%7B8%7DH_%7B18%7D%20%2B%2012.5O_%7B2%7D%20%5Crightarrow%208CO_%7B2%7D%20%2B%209H_%7B2%7DO)