Which gas would you use to support combustion and why?

a. Oxygen

Combustion is, by definition, a chemical reaction in which something (other than oxygen) reacts with oxygen to form a compound (such as CO2 or H2O). So you need oxygen to support the combustion of ANYTHING (wood, gasoline, hydrogen, whatever).

A. Oxygen - oxygen is a necessary component of the fire tetrahedron, along with fuel and heat and ignition. The combination of all these elements creates combustion. A fire goes out when it consumes either the fuel, oxygen or loses heat through cooling such as putting water on it.

Gasses! You listed fuels, not oxidizers. Oxygen is an oxidizer, methane is a fuel. There are several gasses that support combustion and will burn in place of oxygen. Two of them are chlorine and fluorine. Look up HCL burners and how they work and you will see that they burn hydrogen (fuel) and chlorine (oxidizer) in an oxygen free environment. I work in a chemical plant and have a heavy background in chemistry. I suggest you guys take a chemistry class. This is very basic stuff. 😁

Oxygen.

All these answers seem correct to me but I will just add that oxygen also lowers the "kindling" temperature of everything you're trying to ignite or burn.