Which metal cation has the greatest tendency to be reduced (a) pb2+ (b) cr3+ (c) fe2+ (d) sn2+

 (a)

Explanation:

The metal with negative reduction potential will easily lose electrons and thus is oxidized and the one with positive reduction potential will easily gain electrons and thus is reduced.

Where both are standard reduction potentials.

Thus here with negative reduction potential and least magnitude has the most tendency to gain electrons and thus can be most easily reduced.