As per standard reduction potential values, which is the strongest reducing agent among the given elements?

Step-by-step solution

The tendency of an element to lose an electron is measured by its oxidation potential more the value of E ^ of an element stronger will be its reducing character. The alkali metals have a low value of ionization energy which decreases down the group and so can easily lose their valence electrons and thus act as good reducing agent. So, Rb is the strongest reducing agent.