The correct option is: CH4 + O2 → CO2 + H2O.
In writing chemical equations, the reactants are usually written to the left of the equation of the reaction while the products are written to the right of the reaction. An arrow pointing in the right direction shows the direction of the reaction. In the question given above, methane and oxygen are the reactants while carbon dioxide and water are the products. The options that states the chemical reaction correctly is option 1.
