[ShubhamRathi]

The standard potentials of Ag+/Ag, Hg+2/2Hg, Cu2+/Cu and Mg2+/Mg electrodes are 0.80, 0.79, 0.34 and —2.37 V, respectively. An aqueous solution which contains one mole per litre of the salts of each of the four metals is electrolyzed. With increasing voltage, the correct sequence of deposition of the metals at the cathode is :
1)   Mg, Cu, Hg, Ag
2)   Ag, Hg, Cu, Mg
3)   Cu, Hg, Ag only
4)   Ag, Hg, Cu only

Please tell me how this question was solved. What is the concept behind the solving?

[Rutherford]

What does the standard potentials tell you about the ease of the reduction of a metal? What is the reduction potential of water?
If you know this, it should be easy to solve.