Which material is noncombustible and does not burn even in an oxygen-rich atmosphere?

Gypsum is considered noncombustible because it is primarily made of calcium sulfate dihydrate, which does not ignite or burn under normal conditions, even in an oxygen-rich environment. This characteristic is valuable in construction and firefighting, as it helps to prevent the spread of fire. Gypsum boards are widely used as fire-resistant materials in walls and ceilings, helping to create fire barriers that protect structures and occupants.

In contrast, wood, plastic, and steel can behave differently; wood and plastic are combustible materials that will burn when exposed to sufficient heat and oxygen. While steel does not burn, it can lose structural integrity at high temperatures, making it less reliable in fire scenarios than materials specifically designed for fire resistance, such as gypsum. Thus, gypsum’s inherent properties make it the correct choice for a material that does not burn, even in an oxygen-rich atmosphere.