Which one of the following is a combustion reaction?

A. CH4 + 2O2 → CO2 + 2H2O

B. Ba (OH) 2 + 2HClO4 → Ba (ClO4) 2 + 2H2O

C. 4Fe + 4O2 → 2Fe2O3

D. Zn + HCl → ZnCl2 + H2

Combustion reaction is a chemical reaction where compounds and oxidants produce heat and new product during their reaction. The reaction between a HC (hydrocarbon) and O (oxygen) to produce CO2 (carbon dioxide) and H2O (water) is a standard form of a combustion reaction. Therefore, the correct answer would be A. It is the combustion of gas (Methane, CH4) when it encounters oxygen (2O2). Methane will burn forming C02 gas and H20 gas.