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

Reduction potential of copper is higher than zinc

The correct answer is option 4. Reduction potential of copper is higher than zinc.

The standard reduction potential is the reduction potential of a molecule under specific, standard conditions.

Standard reduction potentials can be useful in determining the directionality of a reaction. The reduction potential of a given species can be considered to be the negative of the oxidation potential.

The \(E^0\) values of the copper and zinc electrodes are as follows:

\(Zn^{2+}(aq) + 2e^- \longrightarrow Zn (s),  E^0 = -0.76 V\)

\(Cu^{2+}(aq) + 2e^- \longrightarrow Zn (s),  E^0 = -0.34 V\)

This shows that zinc is a stronger reducing agent than copper. It will lose electrons to \(Cu^{2+}\) ions and a redox reaction will immediately set in.

Copper is less reactive than zinc. Zinc will replace the copper from its salt solution. When the copper sulphate solution is stored in a zinc pot, copper is replaced by zinc, in the copper sulphate solution.

\(Zn + CuSO_4 \longrightarrow ZnSO_4 + Cu\)

So copper sulphate solution cannot be stored in a zinc pot.