Question

how does hydration enthalpy varies from Lithium to caesium

Answer 1

The hydration enthalpy varies from lithium to caesium because lithium being small in size has high ionization enthalpy. On the other hand because of small size it is extensively hydrated and has very high hydration enthalpy. The lithium has greater tendency to lose electrons in solution than other alkali metals. Hence the lithium is the strongest reducing agent.