Answer: Option (a) is the correct answer.
Step-by-step explanation:
An equation can only be balanced when number of reactants equal the number of products.
The given equation is as follows.

The number of reactant atoms are as follows.
The number of product atoms are as follows.
To balance the equation, multiply
by 3, and
by 2 on the reactant side. Multiply
by 6 on the product side. Therefore, the equation will be as follows.

Thus, we can conclude that the coefficient in front of
is 1.