Question

what is the main source of energy for decomposition reaction​

Answer 1

Answer:

This reaction is one of the exceptions to the endothermic nature of decomposition reactions. Other reactions involving decomposition do require the input of external energy. This energy can be in the form of heat, radiation, electricity, or light.

Answer 2

Heat...... Thermal decomposition is the most common type of reaction...

However, heat energy obtained from other source energies (like light) are also notable.