Question

What is the increasing order of hydration enthalpies of alkali metal ions?

• A. $R b^{+}< C s^{-}< K^{+}< N a^{+}< L i^{+}$
• B. $C s^{+}< R b^{+}< K^{+}< L i^{+}< N a^{+}$
• C. $C s^{+}< R b^{+}< K^{+}< N a^{+}< L i^{+}$
• D. $C s^{+}< R b^{+}< N a^{+}< K^{+}< L i^{+}$

Answer 1

Answer: (C)

Hydration enthalpy described as the amount of energy released on dilution of one mole of gaseous ions.
Alkali metals are highly hydrated and the extent of hydration decreases down the group.
The charge density is more for smaller ions and hence, the smaller ions have higher values of hydration enthalpy.
Therefore, increasing order of hydration enthalpies of alkali metals.
$C s^{+}< R b^{+}< K^{+}< N a^{+}< L i^{+}$