Answer
c) is the correct answer.
Work Step by Step
1. The number of Carbon atoms is already equal.
2. Balance the number of Oxygen atoms by changing the coefficient for $H_2O$ from 1 to 2.
$$CH_4(g) + 2 H_2O(g) \longrightarrow H_2(g) + CO_2(g)$$
3. Finally, balance the number of Hydrogen atoms by changing the coefficient from $H_2$ from 1 to 2.
$$CH_4(g) + 2 H_2O(g) \longrightarrow 2H_2(g) + CO_2(g)$$
Therefore, the correct answer is 1,2,2,1. c)
