Answer: Option (a) is the correct answer.
Explanation:
The given reaction is as follows.
[tex]CH_{4} + x(O_{2} + 3.76N_{2}) \rightarrow Products[/tex]
Since, 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.
[tex]CH_{4} + x(O_{2} + 3.76N_{2}) \rightarrow CO_{2} + H_{2}O + 3.76 N_{2}[/tex]
or, [tex]CH_{4} + xO_{2} \rightarrow CO_{2} + H_{2}O[/tex] as nitrogen is not taking part in the reaction.
Number of atoms on reactant side are as follows.
C = 1
H = 4
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 2. Also, we multiply water on product side by 2. Hence, the complete balanced chemical equation is as follows.
[tex]CH_{4} + 2O_{2} \rightarrow CO_{2} + 2H_{2}O[/tex]