The correct answer would be the last option. The chemical reaction that would represent the combustion of methane would be CH4 + 2O2 = CO2 + 2H2O. Combustion reactions are reactions which involves a substance burning in oxygen. It always involve oxygen as a reactant. Usually, it is a reaction of a hydrocarbon and oxygen forming carbon dioxide and water. This type of reaction is a spontaneous reaction which means it happens readily. It does not any supply or input of energy for it to occur. The total kinetic energy of the reactants is equal or greater than the activation energy of the reaction.
