Which among the following reactions is endothermic?

Thermal decomposition

The correct answer is Option (4) → Thermal decomposition

An endothermic reaction is one that absorbs heat from the surroundings.

Let’s analyze the options:

1. Respiration → Exothermic (releases energy)
2. Burning of natural gas → Exothermic (releases energy)
3. Decomposition of vegetable matter into compost → Mostly exothermic (microbial activity releases heat)
4. Thermal decomposition → Endothermic (requires heat to break chemical bonds)