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Charge densities of metal ions decreases down the group. The attraction between the metal ions and the water molecules reduces as a result of reduction of charge densities down the group. The amount of energy released as a result of formation of one mole of aqueous ions from gaseous ions is reduced, which is the basis of hydration enthalpy.
Javan001 answered the question on December 11, 2020 at 18:45
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