Concentration Cell

A concentration cell generates EMF solely from a difference in the concentration of the same ion at the two electrodes, since the electrodes and the electrolyte are chemically identical. The standard cell potential is zero because E°_cathode equals E°_anode; the entire EMF arises from the Nernst concentration term, E_cell = -(0.0591/n) log([dilute]/[concentrated]). The electrode in the more dilute solution acts as the anode and dissolves, raising its ion concentration, while the electrode in the concentrated solution acts as the cathode, where ions deposit and lower the concentration. Current flows until the two concentrations equalise and the EMF falls to zero. The option citing electrode material is wrong because both electrodes are copper. Temperature difference describes a thermal cell, not a concentration cell. Electrode size affects current capacity but not EMF. This is a classic JEE Advanced concentration-cell concept. Examiners frequently test whether a student can connect Nernst equation with the underlying principle rather than merely recalling an isolated fact. It is worth emphasising that this is not a special case but a representative example of how concentration cell operates throughout redox reactions and electrochemistry. Plausibility check: with identical electrodes, only the concentration term in the Nernst equation can supply EMF, confirming the chosen answer.