Which of the following statements are correct for Daniell cell?
A. Zinc electrode is negative terminal.
B. The direction of flow of current is from zinc to copper.
C. Reduction takes place at the copper electrode.
D. Oxidation and reduction half-cells are connected through a salt bridge.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → A, C and D only
The Daniell cell is a galvanic cell made of a zinc rod in \( \ce{ZnSO4} \) solution and a copper rod in \( \ce{CuSO4} \) solution, joined by a salt bridge. It works on the reaction:
\( \displaystyle \ce{Zn(s) + Cu^2+(aq) -> Zn^2+(aq) + Cu(s)} \)
\( \displaystyle \text{Anode (oxidation): }\ce{Zn -> Zn^2+ + 2e-} \)
\( \displaystyle \text{Cathode (reduction): }\ce{Cu^2+ + 2e- -> Cu} \)
In a galvanic cell, oxidation takes place at the anode, which is the negative terminal, and reduction at the cathode, which is the positive terminal. Electrons flow through the external wire from anode to cathode, and conventional current flows in the opposite direction.
A. Zinc electrode is negative terminal. — Correct. Zinc is oxidised and the electrons it releases build up on the rod, so zinc is the anode, the negative terminal.
B. The direction of flow of current is from zinc to copper. — Incorrect. Electrons flow from zinc to copper through the wire, so the current flows from copper to zinc.
C. Reduction takes place at the copper electrode. — Correct. \( \ce{Cu^2+} \) ions gain electrons and deposit as copper metal, so copper is the cathode.
D. Oxidation and reduction half-cells are connected through a salt bridge. — Correct. The salt bridge joins the two solutions, completes the circuit inside the cell and keeps both solutions electrically neutral.
NCERT (2026-27 edition):
Galvanic Cells – “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.”
Fig. 2.1: Daniell cell having electrodes of zinc and copper dipping in the solutions of their respective salts.