(iii) More is oxidation potential, more is the tendency to get oxidized and thus more powerful is reducing nature in aqueous medium that is why alkali metals liberate H₂ from H₂O and HCl.

2H₂O + 2M —> 2MOH + H₂; 2HCl + 2M —> 2MCl + H₂

(iv) However, an examination of ionization energy for alkali metals reveals that Li should have the minimum tendency to lose electron and thus its reducing nature should be minimum. The greatest reducing nature of Li in aq. medium is accounted due to the maximum hydration energy of Li⁺ ion. For Lithium

Li_(s) —> Li_(g), ΔH₁ = Heat of sublimation, ΔH_s

Li_(g) —> Li⁺_(g) ΔH₂ = IE₁

Li⁺_(g) —> Li⁺_(eq); ΔH₃ = – Heat of hydration, DH_h

Li_(s) + H₂O —> Li⁺_(eq) + e; ΔH₁ + ΔH₂ + ΔH₃ = ΔH_s + IE₁ – ΔH_h

Similarly, for sodium,

Na_(s) + H₂O —> Na⁺_(eq) + e; ΔH_(s) + IE₁ – ΔH_h

ΔH_h for Li > ΔH_h for Na. Therefore, large negative ΔH values are observed in case of Li and this explains for more possibility of Li to get itself oxidized or have reducing nature.