The correct option is A Cd(s)|Cd2+(aq, 0.15 M) || Ag+(aq, 0.20 M)|Ag(s)
To get a positive value of the cell potential,
The net ionic equation for the cell reaction is:
2 Ag+(aq)+Cd(s)→Cd2+(aq)+2Ag(s)
In the reaction above, cadmium metal is oxidized (loses electrons) and is, therefore, the anode. The silver ion is reduced (gains electrons) to form Ag (the cathode).
Anode: Cd(s)→Cd2+(aq)+2 e−(oxidation)
Cathode: 2 Ag+(aq)+2 e−→2 Ag(s)(reduction)
cell notation is:
Cd(s) | Cd2+(aq,0.15 M) || Ag+(aq, 0.20 M) | Ag(s)