Which of the given statements for mercury cell are incorrect?

(i)Mercury cell is suitable for low current devices like hearing aids, watches, etc.
(ii)It consists of zinc-mercury amalgam as anode and a paste of HgO and carbon as the cathode.
(iii)The electrolyte is a paste of `Zn(OH)_2` and `KO_2`.
(iv)The electrolyte reactions for the cell are At anode : `Zn(Hg)+ H_2O to ZnO_((s)) + 2OH^(-) + 2e^(-)`
At cathode : `HgO + H_2O + 2e^(-) to Hg_((l)) + 2OH^-`

Options

A. (ii) and (iii) only
B. (i) and (ii) only
C. (i),(iii) and (iv) only
D. (iii) and (iv) only

Answer

D

Explanation

The electrolyte in a mercury cell is a paste of KOH and ZnO. The electrode reactions for the cell are `{:("At anode",Zn(Hg)+2OH^(-) to ZnO_((s))+H_2O+2e^(-)),("At cathode",HgO+H_2O + 2e^(-) to Hg_((l))+2OH^(-)):}`