Concept:A drop in temperature during dissolution shows that heat energy is taken in from the surroundings.Explanation:When NH4Cl dissolves in water, the container feels cold to touch.This cooling effect means heat is absorbed from the water and the container.Any process that absorbs heat from its surroundings is called an endothermic process.Therefore, the dissolution of NH4Cl in water is endothermic.Answer:A. the process is endothermic