The reduction potential values are given below: \[{\text{A}}{{\text{l}}^{{\text{3 + }}}}{\text{/Al = - 1}}{\text{.67volt,M}}{{\text{g}}^{{\text{2 + }}}}{\text{/Mg = - 2}}{\text{.34volt,C}}{{\text{u}}^{{\text{2 + }}}}{\text{/Cu = + 0}}{\text{.34volt,}}{{\text{I}}_{\text{2}}}{\text{/2I - = + 0}}{\text{.53}}\].Which one is the best reducing agent?
A. \[{\text{Al}}\]
B. \[{\text{Mg}}\]
C. \[{\text{Cu}}\]
D. \[{{\text{I}}_2}\]

Hint: Electrochemical the arrangement of elements in order of their increasing electrode potential values. The series is made by measuring the potential of various electrodes with respect to standard hydrogen electrodes (SHE). Standard electrode potential is found by measuring the potential when the half-cell is connected with standard hydrogen electrode under standard conditions.

Complete step by step answer:
When a piece of metal is immersed in a solution of its own ions, a potential difference is developed at the interface of the metal and the solution. The magnitude of this potential difference measures the tendency of electrodes to undergo oxidation (lose electrons) or reduction (gain electrons). If the oxidation takes place at the electrode, it is called the oxidation potential and if reduction takes place at the electrode, it is called the reduction potential.
Oxidation potential = – Reduction potential
The metal which has the most negative reduction potential will lie on the top of electrochemical series. This metal will be the best reducing agent. Here the most negative reduction potential is for magnesium, has hence it is the best reducing agent. Lower the reduction potential, it is a better reducing agent.
Among all these four \[{\text{Mg}}\] is having the least reduction potential so it is the best reducing agent among all four.

Hence, the answer is option B.

Additional information:
The galvanic cell converts chemical energy into electrical energy, by means of redox reaction. It is also known as Daniel cell.

Note: The standard electrode measured by comparing its potential with respect to standard hydrogen electrode (SHE). The arrangement of electrodes in contact with electrolyte solutions based on their standard reduction potential or standard oxidation potentials is called the electrochemical series.