16. When solid ammonium nitrate is dissolved in water, the solution becomes cold. This solution process is: A. Endothermic B. Exothermic C. Neither exothermic nor endothermic D. Not enough information is given

Step 1 ：The dissolution of solid ammonium nitrate in water is associated with a temperature change in the solution.

Step 2 ：When the solution becomes cold, it indicates that the system is absorbing heat from the surroundings.

Step 3 ：This absorption of heat is a characteristic of an endothermic process.

Step 4 ：An endothermic reaction is one that requires energy, usually in the form of heat, from its surroundings to proceed.

Step 5 ：Since the dissolution of ammonium nitrate in water absorbs heat and causes the temperature of the solution to decrease, the correct answer is \(\boxed{\text{Endothermic}}\)