Which of the following ions will have the enthalpy of hydration with the largest magnitude? Which will have the greatest hydration number? Which will be most favored to dissolve in water in terms of entropy?

Ion Sr2 + Cd2 + Cr3+Radius (pm) 132 109 75

Hydration enthalpy increases in magnitude as the ion charge increases and as radius decreases. Of these ions, Cr3 + has both the highest charge and hence the largest magnitude of hydration enthalpy.

It also have the greatest hydration number because the attraction between the ion and water increases with the solute's electric charge and decreases with its radius.

Sr2 + is the most favored to dissolve in water in terms of entropy which is a function of its enthalpy of hydration. Because the energy required to dissolve this ion in water is smaller due to its ionic radius.