What are the reactants and products when butane combusts with excess oxygen? express your answer as a chemical equation?

A combustion reaction involves the reaction of a hydrocarbon with oxygen producing carbon dioxide and water. It would be the same case when butane is reacted with oxygen gas. The reactants would be butane and oxygen and the products are carbon dioxide and water. The balanced chemical reaction would be written as:

C4H10 + 13/2O2 = 4CO2 + 5H2O

So, for every 1 mol of butane combusted, 13/2 moles of oxygen is consumed producing 4 moles of CO2 and 5 moles of water. All combustion reactions are exothermic in nature which means they would release a certain amount of energy in the form of heat energy. This would also be the case for this combustion reaction. 

The answer is d.potassium