Which form of energy causes spontaneous heating of a pile of linseed oil-soaked rags?

The correct answer is chemical energy. Spontaneous heating occurs when a chemical reaction generates heat within a material without an external heat source. In the case of linseed oil-soaked rags, the oil undergoes an oxidation reaction when exposed to air, which can produce enough heat to raise the temperature of the rags. If the heat generated exceeds the heat dissipated, it can lead to spontaneous combustion.

This phenomenon is particularly relevant in situations where materials like oily rags are accumulated, as they can retain heat effectively due to their composition and structure, further contributing to the potential for ignition. Understanding the role of chemical energy in this process is crucial for fire safety and prevention practices in environments where such materials are present.