Which reaction is exothermic?

Explanation:

Exothermic reactions are the reactions in which heat is released. Whereas when there is absorption of heat then the reaction is known as endothermic reaction.

Thus, out of the given chemical equations, the equation CH4 + 2O2 → CO2 + 2H2O + 891 kJ shows that energy has been released. Therefore, this reaction equation is exothermic.

Which reaction is exothermic? CH4 + 2O2 CO2 + 2H2O + 891 kJ NH4NO3 + H2O + 25 kJ NH4+(aq) + NO3-(aq) 2H2O + 286 kJ 2H2 + O2 N2 + O2 + 181 kJ 2NO

Option (a) is the correct answer.