The reaction is endothermic because the temperature dropped from 28 degrees Celsius to 20 degrees Celsius.
An endothermic reaction is one in which heat is absorbed from the surrounding resulting in decrease in temperature while an exothermic reaction is one in which heat is evolved causing the temperature to rise.
In the particular context of this question, the reaction is endothermic because the temperature dropped from 28 degrees Celsius to 20 degrees Celsius. The heat in the surroundings decreased.
Learn more about endothermic reaction: https://brainly.com/question/2192784