Q1. Which of the following is not an exothermic reaction?
A Formation of slaked lime on addition of water to lime
B Burning of natural gas
C Respiration
D Decomposition of calcium carbonate to calcium oxide and carbon dioxide Correct
Explanation
The decomposition of calcium carbonate into calcium oxide and carbon dioxide needs heat, so it is an endothermic reaction and is not exothermic. When water is added to lime, slaked lime forms with the release of heat. Burning natural gas is combustion, and combustion releases heat and light. Respiration is also treated as an exothermic biochemical process because glucose breaks down in cells and releases energy. Therefore, the calcium carbonate decomposition reaction is the only one that does not release heat.