Areaction that releases heat is
1) isothermic
2) endothermic
3) exothermic

A reaction that releases heat is exothermic.

option 3

Explanation:

The exothermic reaction is the one where the heat is evolved or released during the chemical change of the reactants involved occurring as the result of the chemical reaction.

Other types of reaction based on the heat, are an endothermic reaction and isothermic reaction. An endothermic reaction which takes up the heat being absorbed in the reaction. An isothermic reaction where the heat is neither absorbed nor liberated in the reaction.

It is indeed true that being somehow invisible and not very accessible of the groundwater, impose challenge and will not allow people to monitor the affected areas. It is recommended to dig deep well and ask for samples.