Write the electrode reaction and the net cell reaction for the following cells, which electrode would be the positive terminal in each cell?
(a) `Zn|Zn^(2+)||Br^(-),Br_(2)|Pt`
(b). `Cr|Cr^(3+)||I^(-),I_(2)|Pt`.
(c). `Pt|H_(2),H^(+)||Cu^(2+)|Cu`
(d). `Cd|Cd^(2+)||Cl^(-),AgCl|Ag`

Explanation

(a). Oxidation half cell reaction `ZntoZn^(2+)+2e^(-)`
Reduction half cell rection, `Br_(2)+2e^(-)to2Br^(-)`
Net cell reaction `Zn+Br_(2)toZn^(2+)+2Br^(-)` (positive terminal cathode Pt)
(b). Oxidation half reaction, `[CrtoCr^(3+)+3e^(-)]xx2`
reduction half reaction, `[I_(2)+2e^(-)to2I^(-)]xx3`
Net cell reaction `2Cr+3I_(2)to2Cr^(3+)+6I^(-)` (positive terminal cathode Pt)
(c). Oxidation half reaction, `H_(2)to2H^(+)+2e^(-)`
reduction half reaction, `Cu^(2+)+2e^(-)toCu`
Net cell reaction `H_(2)+Cu^(2+)toCu+2H^(+)` (Positive terminal cathode Cu)
(d). Oxidation half raction, `CdtoCd^(2+)+2e^(-)`
reduction half reaction, `[AgCl+e^(-)toAg+Cl^(-)]xx2`
Net cell reaction `Cd+2AgCltoCd^(2)+2Ag+2Cl^(-)` (positive terminal cathode Ag)