Which statement defines spontaneously combustible materials most accurately?

Which statement defines spontaneously combustible materials most accurately?

• A. A material that is non-reactive in air.
• B. A material that is air reactive and can ignite without an external ignition source.
• C. A material that can only ignite underwater.
• D. A material that requires continuous external heat to burn.

Answer: (B)

Spontaneously combustible materials ignite without an external ignition source because they generate heat through reactions with air (oxygen) that can raise their temperature to the point of ignition on their own. The statement describing a material that is reactive in air and can ignite without an outside flame or spark best captures this behavior: it means the material can self-heat and reach ignition temperature in air. If a material is non-reactive in air, it won’t self-ignite. The idea of igniting only underwater isn’t about self-ignition in air, and a material that requires continuous external heat to burn isn’t spontaneous ignition—it needs an outside heat source to start burning.

Spontaneously combustible materials ignite without an external ignition source because they generate heat through reactions with air (oxygen) that can raise their temperature to the point of ignition on their own. The statement describing a material that is reactive in air and can ignite without an outside flame or spark best captures this behavior: it means the material can self-heat and reach ignition temperature in air.

If a material is non-reactive in air, it won’t self-ignite. The idea of igniting only underwater isn’t about self-ignition in air, and a material that requires continuous external heat to burn isn’t spontaneous ignition—it needs an outside heat source to start burning.