The correct answer is H20.
In a chemical reaction, there are always two sides, the reactant side and the product side. The reactants are the elements that are reacting together. They are always written at the left side of a chemical equation, with a plus sign written in between two elements. The products are the new compounds that are formed from the reaction of reactants. They are always written at the right side of a chemical equation and a plus sign is used to join them if they are more than one. An arrow pointing to the products usually connect the two side of the equation. For the question give above, the reactant are CH4 and O2 and the products are CO2 and H2O.
