Which term describes a substance that spontaneously ignites upon exposure to atmospheric oxygen?

Which term describes a substance that spontaneously ignites upon exposure to atmospheric oxygen?

• A. Spontaneous Combustion
• B. Catalytic Material
• C. Pyrophoric Material
• D. Hypergolic Substance

Answer: (C)

A substance that ignites on contact with atmospheric oxygen is described as pyrophoric. These materials react rapidly with air, producing heat enough to reach their ignition temperature without an external flame or spark. This behavior often occurs with finely divided or highly reactive compounds, such as certain alkali metals or organometallics, which ignite in air upon exposure. Other terms don’t fit this behavior. Spontaneous combustion refers to a slow, self-heating oxidation process that can eventually cause ignition, but not necessarily immediate ignition simply from air exposure. A catalytic material speeds up reactions but does not ignite on its own. Hypergolic substances ignite only when they meet a specific oxidizer, not just ordinary atmospheric oxygen.

A substance that ignites on contact with atmospheric oxygen is described as pyrophoric. These materials react rapidly with air, producing heat enough to reach their ignition temperature without an external flame or spark. This behavior often occurs with finely divided or highly reactive compounds, such as certain alkali metals or organometallics, which ignite in air upon exposure.

Other terms don’t fit this behavior. Spontaneous combustion refers to a slow, self-heating oxidation process that can eventually cause ignition, but not necessarily immediate ignition simply from air exposure. A catalytic material speeds up reactions but does not ignite on its own. Hypergolic substances ignite only when they meet a specific oxidizer, not just ordinary atmospheric oxygen.