The half-cell reaction is the one that.......

The correct answer is Option (2) → takes place at one electrode

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. 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: