Read the passage carefully and answer.
When a metal is placed in a solution of its ions, the metal can lose electron and can go in the solution as ion or the metal ion in the solution can take electron from the electrode and get deposited as metal. Thus, the electrode acquires either positive or negative charge with respect to the solution leading to the development of a potential difference between the metal electrode and the solution. This potential difference is called the electrode potential of the metal. The electrode potential of a metal is a measure of relative tendency to undergo oxidation (loss of electron) or reduction (gain of electron). When the concentration of the ions in the solution is unity, the electrode potential is called standard electrode potential. The magnitude of potential depends upon the nature of electrode, concentration of ions in solution and the temperature. In a galvanic cell, the electrode at which oxidation occurs is known as anodic half-cell and the electrode at which reduction occurs is known as cathodic half cell. The emf of the cell in terms of standard reduction potential is given by \( E°_{cell} = E°_{cathode} - E°_{anode} \). The standard free energy change of the redox reaction taking place in the cell is related to \( E°_{cell} \) by \( ΔG°= -nFE° \). A redox reaction would occur spontaneously if the free energy change is negative. The equilibrium constant of the reaction is related to the standard free energy change by \( ΔG°= -RT \ln K \).
The half cell reaction is the one that
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Takes place at one electrode of a Galvanic cell
The redox reaction of a galvanic cell is split into two half reactions: oxidation at one electrode and reduction at the other. Each electrode dipping in its electrolyte is called a half-cell (or redox couple), and the reaction that takes place there is the half-cell reaction. So a half-cell reaction is the one that takes place at one electrode of a galvanic cell. The word “half” refers to one of the two parts of the cell reaction, not to half a mole, half the concentration or half the potential.
NCERT (2026-27 edition):
Galvanic Cells – “… Daniell cell discussed earlier is one such cell in which the following redox reaction occurs.
\( \ce{Zn(s) + Cu^2+(aq) -> Zn^2+(aq) + Cu(s)} \)
This reaction is a combination of two half reactions whose addition gives the overall cell reaction:
(i) \( \ce{Cu^2+ + 2e^- -> Cu(s)} \) (reduction half reaction)
(ii) \( \ce{Zn(s) -> Zn^2+ + 2e^-} \) (oxidation half reaction)
These reactions occur in two different portions of the Daniell cell. The reduction half reaction occurs on the copper electrode while the oxidation half reaction occurs on the zinc electrode. These two portions of the cell are also called half-cells or redox couples. The copper electrode may be called the reduction half cell and the zinc electrode, the oxidation half-cell.”
Note: The same/similar question has been asked in different years by NTA as per the details given below:
| 2026 | 2025 | 2024 | 2023 | 2022 |
|---|---|---|---|---|
| – | 14-05 S1 13-05 S2 | – | – | – |