For the cell Zn | Zn2+(1 M) || Cu2+(1 M) | Cu, E°cell = 1.10 V. There…

The correct answer is Option (4) → \(Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu\) is spontaneous

• In the cell notation the left electrode is the anode (oxidation) and the right electrode is the cathode (reduction):

      Anode: \( \displaystyle \ce{Zn(s) -> Zn^2+(aq) + 2e^-} \)
      Cathode: \( \displaystyle \ce{Cu^2+(aq) + 2e^- -> Cu(s)} \)
      Cell reaction: \( \displaystyle \ce{Zn(s) + Cu^2+(aq) -> Zn^2+(aq) + Cu(s)} \)

• The standard Gibbs energy of the cell reaction follows from the cell potential, with n = 2:

      \( \displaystyle \Delta_rG^{\circ}=-nFE^{\circ}_{\text{cell}} \)

      \( \displaystyle \Delta_rG^{\circ}=-2\times96487\,\mathrm{C\,mol^{-1}}\times1.10\,\mathrm{V}=-212.27\,\mathrm{kJ\,mol^{-1}} \)

• A positive E°_cell gives a negative Δ_rG°, so the reaction of zinc with \( \ce{Cu^2+} \) ions is spontaneous. This is the reaction that runs on its own in the Daniell cell and gives electrical energy.

Why the other options are incorrect

Option (1) \(Zn + Cu^{2+} \rightarrow Zn^{2+} + Cu\) cannot occur — Incorrect. This is the cell’s own reaction; with E°_cell = +1.10 V it takes place on its own.

Option (2) \(Zn^{2+} + Cu \rightarrow Zn + Cu^{2+}\) is spontaneous — Incorrect. This is the reverse reaction. Its E° is −1.10 V, so Δ_rG° is positive and it is non-spontaneous; it is driven only when an external voltage greater than 1.1 V is applied.

Option (3) \(Cu + Zn^{2+} \rightarrow Cu^{2+} + Zn\) is sluggish — Incorrect. E°_cell tells the direction of the reaction, not its speed. This reverse reaction does not go on its own at all, so it is not merely slow.

NCERT (2026-27 edition):
2.1 Electrochemical Cells – “We had studied the construction and functioning of Daniell cell …. This cell converts the chemical energy liberated during the redox reaction

    \( \displaystyle \ce{Zn(s) + Cu^2+(aq) -> Zn^2+(aq) + Cu(s)} \qquad (2.1) \)

to electrical energy and has an electrical potential equal to 1.1 V when concentration of Zn²⁺ and Cu²⁺ ions is unity (1 mol dm^–3). Such a device is called a galvanic or a voltaic cell.”

2.2 Galvanic Cells – “As mentioned earlier a galvanic cell is an electrochemical cell that converts the chemical energy of a spontaneous redox reaction into electrical energy.”