Consider the galvanic cell Zn|\[{\rm{ZnS}}{{\rm{O}}_{\rm{4}}}\] ||\[{\rm{CuS}}{{\rm{O}}_{\rm{4}}}\]|Cu, the reaction at cathode is:
A. \[{\rm{C}}{{\rm{u}}^{{\rm{2 + }}}} + {\rm{2}}{{\rm{e}}^ - } \to {\rm{Cu}}\]
B. \[{\rm{Z}}{{\rm{n}}^{{\rm{2 + }}}} + 2{e^ - } \to {\rm{Zn}}\]
C. \[{\rm{C}}{{\rm{u}}^{{\rm{2 + }}}} + {\rm{Zn}} \to {\rm{Cu}} + {\rm{Z}}{{\rm{n}}^{2 + }}\]
D. \[{\rm{Z}}{{\rm{n}}^{{\rm{2 + }}}} + {\rm{Cu}} \to {\rm{Zn}} + {\rm{C}}{{\rm{u}}^{2 + }}\]

Hint: The electrochemical cell defines the cell that produces electricity from the chemical reaction. A dry cell or we can say a battery used mostly in the portable electronic device and equipment of houses. The copper zinc cell is an electrochemical cell.

Complete Step by Step Solution:
Let's understand copper-zinc cell in detail. This cell can be prepared from zinc and copper metal with sulphate solution of each. That means, that a zinc electrode is placed in the solution of zinc sulphate and a copper electrode is dipped in the solution of copper sulphate and these two solutions (copper sulphate and zinc sulphate) are connected with the help of a salt bridge. And the two electrodes are connected by wires.

The oxidation reaction happens at the anode of zinc. Zinc lost two numbers of electrons and form cations and the reaction is,
 \[{\rm{Zn}} \to {\rm{Z}}{{\rm{n}}^{2 + }} + 2{e^ - }\]

The reduction reaction happens at the cathode of copper. The copper ions take up electrons to form copper metal and get deposited. The chemical reaction is,
\[{\rm{C}}{{\rm{u}}^{{\rm{2 + }}}} + 2{e^ - } \to {\rm{Cu}}\]

Also, from the given cell notation we can identify the reaction of the cathode. In cell notation, the reaction of the cathode is always present at the right-hand side.
Therefore, in the Cu-Zn cell, the reaction occurs at cathode is \[{\rm{C}}{{\rm{u}}^{{\rm{2 + }}}} + 2{e^ - } \to {\rm{Cu}}\].
Hence, option A is right.

Additional Information: Let's understand the process of electrolysis. A process in which the passing of electricity takes place through electrolytes and a chemical reaction occurs is termed electrolysis. And a device that generates electricity through the electrolysis process is termed a galvanic cell or electrochemical cell. In the process of electrolysis in a galvanic cell, the conversion of chemical energy to electrical energy takes place.

Note: Electrochemical cells are divided into two types namely electrolytic and galvanic cells. An electrolytic cell does the work of conversion of electrical energy to chemical energy. But in a galvanic cell, the chemical energy converts to electrical energy.