The correct option is B Cu displaces Mg from MgSO4
Standard reduction potentials (SRP) of the half cell electrodes are calculated and arranged in a series of increasing order which is known as electrochemical series.
The standard electrode potential of H+/H2 couple is zero.
Here, a negative E0 signifies that it has high tendency to get oxidised and the redox couple is a stronger reducing agent than the H+/H2 couple.
A positive E0 signifies that it has high tendency to get reduced and the redox couple is a stronger oxidising agent than the H+/H2 couple.
Mg2+/Mg couple has less E0 value than Cu2+/Cu. So, Cu2+ gets reduced and has higher oxidising power than Mg2+
For Mg(s) to reduce CuSO4(aq), the following reaction's E0cell must be positive.
E0cell=SRP cathode- SRP anode
E0cell=E0Cu2+/Cu−E0Mg2+/MgE0cell=(0.34−(−2.36)) VE0cell=+2.7 V
Thus option (d) is correct.
E0cell value for the reverse reaction is negative :
So, MgSO4 can be stored in Cu vessel
Thus, statement (b) is incorrect.