If an endothermic reaction occurs in water, the relationship of the water's final temperature, tf, to its initial temperature, ti, will be

Final temperature of water is lesser.

Explanation:

An endothermic reaction means that reactant absorbs heat from surroundings, meaning that temperature of water decreases for the endothermic reaction.

In endothermic reaction heat was absorbed, so the reaction will absorb heat from water so the final temperature of water is less than initial temperature

Tf < Ti