Assertion : Mercury cell does not give steady potential.

Reason : In the cell reaction, ions are not involved in solution.

(v) Assertion is false but reason is true.

The overall reaction of Mercury cell is represented as

Zn(Hg) + HgO_(S) → ZnO_(S) + Hg_(l)

The cell potential value is ~1.35V and remains constant throughout its life as they do not involve any ion whose concentration varies during its lifetime. Thus, gives a steady potential throughout its life.