E°cell for the reaction Mg + Ni2+ → Mg2+ + Ni is positive. Which of t…

The correct answer is Option (4) → E°_cell for the reaction Ni + Mg²⁺ → Ni²⁺ + Mg is positive.

The cell potential is the reduction potential of the cathode minus that of the anode. A positive E°_cell gives a negative Δ_rG° (Δ_rG° = −nFE°_cell), so the reaction as written is spontaneous:

    \( \displaystyle \ce{Mg(s) + Ni^2+(aq) -> Mg^2+(aq) + Ni(s)} \)

• Here magnesium is oxidised (anode) and \( \ce{Ni^2+} \) is reduced (cathode).

• Writing the reaction the other way round swaps the cathode and the anode, so E°_cell keeps its size but changes sign.

Option (1) When a strip of magnesium is placed in a nickel salt solution, nickel is deposited spontaneously. — Correct statement. This is the given spontaneous reaction: Mg goes into solution as \( \ce{Mg^2+} \) and Ni metal is deposited.

Option (2) Nickel atoms will not spontaneously give electrons to magnesium ions. — Correct statement. That would be the reverse reaction, which has a negative E°_cell and is not spontaneous.

Option (3) Magnesium is more electropositive than nickel. — Correct statement. Magnesium gives up its electrons to \( \ce{Ni^2+} \), so it loses electrons more readily than nickel.

Option (4) E°_cell for the reaction Ni + Mg²⁺ → Ni²⁺ + Mg is positive. — Incorrect statement. In the reversed reaction Ni is the anode and Mg²⁺/Mg the cathode, so E°_cell has the same size but a negative sign.

NCERT (2026-27 edition):
2.2 Galvanic Cells – “… The cell potential is the difference between the electrode potentials (reduction potentials) of the cathode and anode. … It is now an accepted convention that we keep the anode on the left and the cathode on the right while representing the galvanic cell. … Under this convention the emf of the cell is positive and is given by the potential of the half-cell on the right hand side minus the potential of the half-cell on the left hand side i.e.,

    \( \displaystyle E_{\text{cell}}=E_{\text{right}}-E_{\text{left}} \)”