The electrochemical series gives a relative strength arrangement of standard electrode reduction potentials of common ions and elements. It is arranged in increasing order of Reduction Potential from bottom to top with F being at the top and Li being at the bottom.

Now whether a reaction should takes place or not would depend on the net cell EMF of the cell, given by equation

Option (i)Cu + Zn²⁺→ Cu²⁺ + Zn

Here Cu undergoes oxidation so it acts as anode and Zn acts as cathode. So from the table

For cathode E°_cathode = -0.76 V

For anode E°_anode = 0.52 V

As the EMF of cell is negative the given reaction will not occur spontaneously if they were to form a cell placed as electrodes.

Option (ii) Mg + Fe²⁺→ Mg²⁺ + Fe

Similarly, we can say that Mg undergoes oxidation and Fe undergoes reduction.

E°_cathode = -0.44 V

E°_anode = -2.36 V

Positive EMF implies that the reaction will give out energy and attain stability, thus it will occur spontaneously. So the given redox reaction will occur.

Option (iii) Br₂ + 2Cl^-→ Cl₂ + 2Br^-

Here Br undergoes reduction thus acting as cathode and Cl acting as anode.

For cathode E°_cathode = 1.09 V

For anode E°_anode = 1.36 V

The negative potential prevents easy reaction, so the redox reaction will not occur.

Option (iv) Fe + Cd²⁺→ Cd + Fe²⁺

Fe is the cathode and Cd is the anode

For cathode E°_cathode = -0.44 V

For anode E°_anode = -0.40 V

The negative potential prevents easy reaction, so the redox reaction will not occur.