A solution of copper sulphate cannot be stored in zinc vessel because

The correct answer is Option (4) → Reduction potential of copper is higher than zinc

A metal with a lower (more negative) standard reduction potential is a stronger reducing agent; it displaces a metal of higher reduction potential from a solution of its salt. The values are:

    \( E^\circ_{\ce{Cu^2+/Cu}} = +0.34\ \mathrm{V} \qquad E^\circ_{\ce{Zn^2+/Zn}} = -0.76\ \mathrm{V} \)

Since copper has the higher reduction potential, \( \ce{Cu^{2+}} \) ions are reduced by zinc, and the zinc vessel dissolves:

    \( \ce{Zn(s) + CuSO4(aq) -> ZnSO4(aq) + Cu(s)} \)

    \( E^\circ_{\text{cell}} = 0.34 - (-0.76) = 1.10\ \mathrm{V} \) (positive, so the reaction is spontaneous)

This is the reaction of the Daniell cell. So copper sulphate solution cannot be kept in a zinc vessel.

Why the other options are incorrect

• Option (1) Copper is more reactive than zinc — Incorrect. The reverse is true; zinc is more reactive and displaces copper.

• Option (2) Reduction potential of copper is less than zinc — Incorrect. Copper’s reduction potential (+0.34 V) is higher than zinc’s (−0.76 V); if it were lower, no reaction would occur.

• Option (3) Oxidation potential of copper is higher than zinc — Incorrect. The oxidation potential is the reduction potential with the sign changed: Cu −0.34 V, Zn +0.76 V; zinc’s is higher, which is why zinc is the one oxidised.

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

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

“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.”