What causes white phosphorous to ignite?

White phosphorus ignites due to its reaction with oxygen when it comes into contact with air. This highly reactive substance has a low ignition temperature and is prone to spontaneous combustion in an atmospheric environment. The exposure to air allows the phosphorus to oxidize rapidly, producing enough heat to ignite the material.

While other options suggest different scenarios for ignition, they do not apply to white phosphorus. High temperatures are not necessary for ignition, as white phosphorus can catch fire at room temperature when exposed to air. Additionally, there is no requirement for a catalyst to spark combustion, and contrary to any misconceptions, white phosphorus does not combust spontaneously in water; instead, it usually reacts violently in certain conditions. Therefore, the correct choice emphasizes the specific nature of white phosphorus reactivity with oxygen in the air.