Which one of the following is an endothermic reaction ?

An endothermic reaction is a chemical process in which the system absorbs energy from its surroundings, typically in the form of heat [3]. Decomposition reactions generally require energy input—such as heat, light, or electricity—to break chemical bonds, making them endothermic [4]. Specifically, the thermal decomposition of lead(II) nitrate into lead oxide, nitrogen dioxide, and oxygen requires heating to proceed [1]. In contrast, the other options represent exothermic processes: the combustion of methane (Option 1) releases significant thermal energy [1]; the oxidation of glucose (respiration, Option 2) is a known exothermic process that provides energy to living cells [2]; and the synthesis of ammonia (Haber process, Option 3) is also exothermic, releasing heat as products form [4]. Therefore, the decomposition of lead nitrate is the only endothermic reaction listed.

Sources

1. [3] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > What you have learnt > p. 14
2. [4] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > Activity 1.8 > p. 10
3. [1] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > Activity 1.6 > p. 9
4. [2] Science , class X (NCERT 2025 ed.) > Chapter 1: Chemical Reactions and Equations > C6H12O6 (aq) + 6O2 (aq) → 6CO2 (aq) + 6H2O(l) + energy (1.18) (Glucose) > p. 7