Question

Assertion: In mercury cells, the cell potential is approximately 1.35 V and remains constant during its life.
Reason: The overall reaction in the mercury cell is represented as
\[Zn(s) + HgO(s) \to ZnO(s) + Hg(l)\]
(A) Both assertion and reason are correct and the reason is the correct explanation for the assertion.
(B) Both assertion and reason are correct but the reason is not the correct explanation for the assertion.
(C) Assertion is correct but reason is incorrect
(D) Both the assertion and the reason are incorrect.

Answer 1

Hint: In order to answer whether the given assertion and reason are correct or incorrect, we must be knowing about mercury cells. Mercury cells can also be referred to as mercuric oxide. Mercury cell is a primary cell which will be used and later on discarded. It is a non-rechargeable cell.

Complete Solution :
Let us first understand what a cell is. Cell is a single unit of device which can convert the chemical energy into electrical energy. A group of cells will be combined to form a battery. Mercury cells which are also referred to as mercuric oxide will come under the primary cell. The primary is a non-rechargeable cell. Mercury cells will be using a reaction between the mercuric oxide and zinc electrode. The reaction will be occurring in an alkaline solution. The reaction of the mercury cell is given below:
\[Zn(s) + HgO(s) \to ZnO(s) + Hg(l)\]

- From the above reaction, we can see that there are no ions formed in the reaction, therefore the concentration of the solution will remain constant. Since there is no change in the concentration the cell potential will also remain as 1.35 V throughout its shell life.
- From this we can say that the Assertion and the reason given are correct. Therefore, the reason is the correct explanation for the assertion.
So, the correct answer is “Option B”.

Note: We should remember that the primary cell and the secondary cell are different from each other. Primary cell is usually a non-rechargeable cell while the secondary cell can be recharged. The primary cell can be discarded after the one time use while the secondary cell is used till their shell life.