Most powerful and least powerful reducing agents of alkali metals are ____ and ______ respectively (Based on ${\mathrm{E}}_{S\mathrm{RP}}^0$ values)

The alkali metals are strong reducing agent due to there tendency to lose electron.

The reducing strength increases down the group.

However the reducing strength of Li is more Than that of Na due to the higher hydration energy of Li.

Thus the correct order will be:

Li > Na < K < Rb <Cs

Thus, least powerful reducing agent is Na