Atomic size generally decreases as you move from left to right across a period because as fast as it goes it will always be slower than generally the size.
When a stable atom gains or loses its electrons then that’s when it becomes the ion.
Answer:
Endothermic.
Explanation:
Because the temperature decreased, the reaction is endothermic.
Endothermic reactions absorb heat from the surroundings. In this case, the dissolution of the ammonium nitrate absorbed heat from the surroundings (the water). Hence, the temperature of the solution decreased.