Concept:For an ionic compound to dissolve in water, the energy released by hydration must be greater than the energy holding the crystal together, called lattice energy.
Explanation:MgO is an ionic compound made of
Mg2+ and
O2− ions.
These ions are small and have high charges, so the electrostatic forces between them are very strong.
As a result,
MgO has an extremely high lattice energy.
When
MgO is put in water, water molecules try to surround and hydrate the ions.
However, the hydration energy released is not large enough to overcome the strong lattice energy.
Therefore, the crystal structure of
MgO remains intact and it does not readily dissolve in water.
This makes lattice energy greater than hydration energy the correct reason.
Answer:D. its lattice energy is higher than its hydration energy