Write the cell reactions for the following cells.
(i) `Zn|ZnO_(2)^(2-), OH^(-)|HgO|Hg`
(ii) `Pb|PbSO_(4)|H_(2)SO_(4)|PbSO_(4)|PbO_(2)|Pt`
(iii) `Pt|H_(2)|HCl|Hg_(2)Cl_(2)|Hg|Pt`

Explanation

(i) The electrode reactions are
`Zn_((s))+4OH^(-)+2e^(-)rarr ZnO_(2)^(2-)+2H_(2)O`
`HgO_((s))+H_(2)O+2e^(-)rarr Hg_((s))+2OH^(-)`
Cell reaction is
`Zn_((s))+HgO_((s))+2OH^(-)rarr ZnO_(2)^(2-)+Hg_((s))+H_(2)O`
(ii) The electrode reactions are
`Pb_((s))+SO_(4)^(2-)rarr PbSO_(4(s))+2e^(-)`
`PbO_(2(s))+SO_(4)^(2-)+4H^(+)+2e^(-)rarr PbSO_(4(s))+2H_(2)O`
Cell reaction is
`Pb_((s))+PbO_(2(s))+4H^(+)+2SO_(4)^(2-)rarr 2PbSO_(4(s))+2H_(2)O`
(iii) The electrode reaction are
`2H^(+)+2e^(-)rarr H_(2(g))`
`Hg_(2)Cl_(2(s))+2e^(-)rarr 2Hg_((l))+2Cl^(-)`
The cell reaction is
`Hg_(2)Cl_(2(s))+H_(2)rarr 2Hg_((l))+2H^(+)+2Cl^(-)`