In level 2, you balanced the equation C + H2O → CH4 + CO2. What number did you place in front of carbon dioxide (CO2)?

Let the coefficient of CO2 be 1. That gives 2 oxygen atoms on the right, so place 2 before H2O. The 4 hydrogen atoms then require 1 before CH4, and the carbon atoms balance with 2 before C. Thus the coefficient in front of carbon dioxide is 1, choice A.

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