The process that occurs when heat is generated by a chemical reaction within a substance and continues to a point of ignition is known as __________.

Correct Answer: Option D — spontaneous combustion

Spontaneous combustion is the process where internal chemical reactions generate sufficient heat to reach the ignition temperature of a material. This often occurs in poorly ventilated spaces where heat accumulation from slow oxidation processes leads to a self-sustaining fire without an external ignition source.