Ncert Exercises & Solutions

Assertion (A):	Mercury cell does not give steady potential.
Reason (R):	In the cell reaction, ions are not involved in the solution.

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	(A) is false but (R) is true.

Hint: Mercury cell gives steady potential.

The overall reaction is represented by:

Zn(Hg) + HgO(s) ---> ZnO(s) + Hg(l)

Mercury cell gives steady potential. The cell potential remains constant during its life as the overall reaction does not involve

any ion in a solution whose concentration can change during its lifetime.

Hence, the Assertion is false but the reason is true.