What defines "ignition temperature"?

The concept of "ignition temperature" is defined as the minimum temperature required for a substance to ignite and sustain combustion without the need for an external ignition source like a flame or spark. This means that once the substance reaches this temperature, it has the potential to start burning on its own due to the thermal energy supplied. Understanding this is crucial in safety and hazard assessments, as it helps determine the conditions under which materials may ignite in various environments.

The other options do not accurately convey the meaning of ignition temperature. For example, a temperature that prevents combustion would imply that ignition cannot occur at all, which is the opposite of the concept of ignition temperature. The ideal temperature for chemical reactions refers to different thermodynamic conditions that facilitate reactions but do not specifically pertain to the initiation of combustion. Lastly, a temperature below which materials cannot combust would imply a threshold that would lead to no possibility of ignition, which again is not what ignition temperature signifies.