Chemistry - Electrochemistry Question with Solution | TestHub

The standard emf of a cell is given by $E_{\text{cell}}^{\circ }=E_{\text{cathode}}^{\circ }-E_{\text{anode}}^{\circ }$.

To obtain the maximum standard emf, the cathode must have the highest standard reduction potential and the anode must have the lowest standard reduction potential.

Given standard reduction potentials are:
$E_{\text{A}}^{\circ }=+2.5\text{ V}$
$E_{\text{B}}^{\circ }=+3.0\text{ V}$
$E_{\text{C}}^{\circ }=-2.0\text{ V}$
$E_{\text{D}}^{\circ }=-1.5\text{ V}$

The highest reduction potential is for electrode B ($+3.0\text{ V}$), so B should act as the cathode.

The lowest reduction potential is for electrode C ($-2.0\text{ V}$), so C should act as the anode.

Maximum $E_{\text{cell}}^{\circ }=3.0-(-2.0)=5.0\text{ V}$.

Thus, 'C' is the anode and 'B' is the cathode.

Answer: 'C' is anode and 'B' is cathode