Which of the following is an exothermic reaction?

All of these

The correct answer is option 4. All of these.

Examples of exothermic reactions are –

(i) Burning of natural gas (methane)

CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (g)

(ii) Respiration is an exothermic process. We all know that we need energy to stay alive. We get this energy from the food we eat. During digestion, food is broken down into simpler substances. For example, rice, potatoes and bread contain carbohydrates. These carbohydrates are broken down to form glucose. This glucose combines with oxygen in the cells of our body and provides energy. The special name of this reaction is respiration

C₆H₁₂O₆(aq) + 6O₂(aq) → 6CO₂(aq) + 6H₂O(l) + energy

(Glucose)

(iii) The decomposition of vegetable matter into compost is also an example of an exothermic reaction.