Under which conditions, if any, will gypsum burn?

Gypsum, chemically known as calcium sulfate dihydrate, is a mineral that can withstand high temperatures and is generally considered a fire-resistant material. It does not burn easily and has a low combustion potential due to its composition. When exposed to fire, gypsum can dehydrate and release water vapor, which can actually help in cooling and suppressing flames.

Saying that gypsum has limited combustibility acknowledges that while it is not completely non-combustible, it does not behave like typical combustible materials such as wood or paper. Instead, gypsum is often used in fireproofing applications, such as fire-rated wall assemblies, because of its ability to delay the spread of fire and its minimal contribution to flame propagation.

The other options reference conditions that do not typically lead to the combustion of gypsum, as it does not burn under normal atmospheric conditions, nor does it ignite with simply an increased oxygen supply. Thus, the accurate characterization of gypsum's behavior in fire situations is that it is not easily combustible, supporting the understanding that it has limited combustibility.