Lithium is strongest reducing agent among alkali metals due to which of the following factor?

The correct option is C

Hydration energy

Higher heat of hydration of $L{i}^{+}$ ion is responsible for greater –ve magnitude for the heat of the reaction which is the sum of $H_s$ + I.E -$H_n$. Reducing ability depends on various factors such as sublimation energy, ionization energy, hydration energy.