3. The molar heat of solution for ammonium nitrate (NH 4 NO 3 ) is 25.7 kJ/mol.
How many moles of NH 4 NO 3 (s) must be dissolved in water so that 88.0 kJ of
heat is released from the water (this process is endothermic -- the heat is
being absorbed as the ions break apart)

Explanation:

By the law of conservation of  energy, assuming no losses of heat to the surroundings, the amount of heat consumed by the dissolution of the ammonium nitrate is equal to the amount of heat released from the water.  This is, the ammonium nitrate absorbs all the heat it needs to break the ions apart and get dissolved from the water in which it is being dissolved.

Thus:

         ↑                           ↑                                        ↑

heat released      number of moles             molar heat of solution

from water           of NH₄NO₃                        for NH₄NO₃

Solve for n and compute:

c) should be the answer.