Concept:The solubility of an ionic compound depends on the relative strengths of its lattice energy and hydration energy.
Explanation:When an ionic salt dissolves in water, its crystal lattice must be broken and the released ions must be hydrated by water molecules.
If the lattice energy is much higher than the hydration energy, the compound dissolves only to a small extent.
General solubility rules state that most chlorides are soluble, so
CaCl2 and
NaCl dissolve freely.
Sodium salts are also usually soluble, hence
Na2SO4 shows good solubility.
However,
CaSO4 is a well-known exception among sulfates.
Its relatively high lattice energy makes it sparingly soluble in water.
Therefore, among the listed salts, calcium sulfate has the lowest solubility.
Answer:CaSO4 (Calcium sulfate) is the least soluble compound, so the correct option is B.