Concept:Dissolving or hydration involves energy changes related to breaking the crystal lattice and hydrating the ions.
Explanation:Lattice energy is the energy required to separate the ions in a crystal, so it is absorbed (endothermic).
Hydration energy is the energy released when ions are surrounded by water molecules (exothermic).
When the hydration energy is greater than the lattice energy, the total energy released exceeds the energy absorbed.
This makes the overall enthalpy change negative, so the process gives out heat to the surroundings.
A reaction that releases heat is called an exothermic reaction.
Answer:C. an exothermic reaction