Which of the following reactions are exothermic? 1) C + O2 → CO22) 2Mg + O2 → 2MgO3) CuSO4 + 5H2O → CuSO4.5H2O4) All the above

Here all the given options are Exothermic reactions. Exothermic reactions are those reactions which involves the release of heat.

Generally all the combining reactions are exothermic in nature.