Q10 / 150 · MHT CET 2026 (18 April Shift 2) · Chemistry
If standard reduction potential of four electrodes A, B, C, D are $+2.5\,\text{V}, +3.0\,\text{V}, -2.0\,\text{V}$ and $-1.5\,\text{V}$ respectively. When is the standard emf of cell maximum?
- A'A' is anode and 'B' is cathode
- B'B' is anode and 'D' is cathode
- Correct answerC'C' is anode and 'B' is cathode
- D'B' is anode and 'C' is cathode
Solution
The standard emf of a cell is given by $E^{\circ}_{\text{cell}} = E^{\circ}_{\text{cathode}} - E^{\circ}_{\text{anode}}$.
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:
$E^{\circ}_{\text{A}} = +2.5\text{ V}$
$E^{\circ}_{\text{B}} = +3.0\text{ V}$
$E^{\circ}_{\text{C}} = -2.0\text{ V}$
$E^{\circ}_{\text{D}} = -1.5\text{ V}$
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 $E^{\circ}_{\text{cell}} = 3.0 - (-2.0) = 5.0\text{ V}$.
Thus, 'C' is the anode and 'B' is the cathode.
Answer: 'C' is anode and 'B' is cathode
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:
$E^{\circ}_{\text{A}} = +2.5\text{ V}$
$E^{\circ}_{\text{B}} = +3.0\text{ V}$
$E^{\circ}_{\text{C}} = -2.0\text{ V}$
$E^{\circ}_{\text{D}} = -1.5\text{ V}$
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 $E^{\circ}_{\text{cell}} = 3.0 - (-2.0) = 5.0\text{ V}$.
Thus, 'C' is the anode and 'B' is the cathode.
Answer: 'C' is anode and 'B' is cathode
Hence, the correct answer is option: 'C'.