When the temperature of water decreases by dissolving crcl2, the reaction is endothermic reaction.
The two types of reaction that are opposite to each other are endothermic and exothermic reaction. Endo means inside and Exo means outside and thermic refers to heat.
So, in Exothermic reaction, heat is released and the temperature increases and in endothermic reaction, heat is absorbed and and the temperature decreases. So, this reaction or process is endothermic because by adding CrCl2, the temperature decreases.