Consider the following statements about the Nernst equation and the D…

The correct answer is Option (2) → (C) and (D) only

For the Daniell cell, \( \ce{Zn(s) + Cu^2+(aq) -> Zn^2+(aq) + Cu(s)} \), the Nernst equation at 298 K is

    \( \displaystyle E_{cell} = E^{\circ}_{cell} - \frac{0.059}{2}\log\frac{[\ce{Zn^2+}]}{[\ce{Cu^2+}]} \)

(A) The E_cell of a Daniell cell increases with an increase in the concentration of Cu²⁺ ions and a decrease in the concentration of Zn²⁺ ions. — Correct statement. A larger [Cu²⁺] or a smaller [Zn²⁺] makes the log term smaller, so E_cell rises.

(B) When a Daniell cell attains equilibrium, the voltmeter gives zero reading and the concentrations of Cu²⁺ and Zn²⁺ ions show no further change. — Correct statement. At equilibrium E_cell = 0, so there is no further net reaction and the concentrations stay constant.

(C) When the circuit of a Daniell cell is closed, the concentration of Zn²⁺ ions keeps on decreasing while the concentration of Cu²⁺ ions keeps on increasing. — Incorrect statement. Zinc dissolves as Zn²⁺ and Cu²⁺ is deposited as copper, so [Zn²⁺] keeps on increasing and [Cu²⁺] keeps on decreasing; the voltage falls as this goes on.

(D) In writing the Nernst equation for a cell, a different number of electrons (n) is used for each of the two electrodes. — Incorrect statement. The same number of electrons (n) is used for both electrodes, the number transferred in the balanced cell reaction (for example n = 2 for \( \ce{Ni(s) + 2Ag+(aq) -> Ni^2+(aq) + 2Ag(s)} \)).

NCERT (2026-27 edition):
2.3 Nernst Equation – “…It can be seen that E_(cell) depends on the concentration of both Cu²⁺ and Zn²⁺ ions. It increases with increase in the concentration of Cu²⁺ ions and decrease in the concentration of Zn²⁺ ions.”

“…We should use the same number of electrons (n) for both the electrodes…”

2.3.1 Equilibrium Constant from Nernst Equation – “If the circuit in Daniell cell … is closed then we note that the reaction Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s) takes place and as time passes, the concentration of Zn²⁺ keeps on increasing while the concentration of Cu²⁺ keeps on decreasing. At the same time voltage of the cell as read on the voltmeter keeps on decreasing. After some time, we shall note that there is no change in the concentration of Cu²⁺ and Zn²⁺ ions and at the same time, voltmeter gives zero reading. This indicates that equilibrium has been attained.”