An aqueous solution containing `Cu^(2+), Hg_(2)^(2+) and Ag^(+)` ions, each with a concentration of 1M, is being electrolysed by using Pt - electrodes. If the voltage between the electrodes is increased gradually, which one of these ions will be deposited first and which one will be deposited last at the cathode?
`E_(Ag^(+)|Ag)^(@)=0.8V, E_(Cu^(+)|Cu)^(@)=0.34V & E_(Hg^(+)|2Hg)^(@)=0.79`

Explanation

We know a redox couple with higher standard electrode potential is stronger oxidising agent than that one with lower `E^(@)` i.e., electrode with higher standard reduction potential tends to get reduced much faster. Among the given electrodes `Ag^(+)|Ag` has the highest `E^(@)` value and `Cu^(+)|Cu` has the lowest `E^(@)` value. Thus `Ag^(+)` will be reduced first followed by `Hg_(2)^(2+) and Cu^(2+)`.