Find the `EMF ` of the cell at `25^(@)C`.
`E^(c-)._(red("quinhydrone electrode ")=0.699V`
`E^(c-)._(red(" calomel electrode")=+0.268V`.

Explanation

For calomel electrode `:`
`Hg_(2)Cl_(2)(s)+2e^(-1) rarr 2Hg+2Cl^(c-)`
For decinormal calomel electrode `: [Cl^(c-)]=0.1N`
`E_((red)) ` Calomel`=E^(c-)-(0.059)/(2)log [Cl^(c-)]^(2)`
`=0.268-(0.059)/(2)log[0.1]^(2)`
`=0.268+0.059=0.327V`
For quinhydrone electrode, `i.e., Pt |H_(2)Q|H^(o+)|Q`

`E_(red(qui nhydron e))=E^(c-)-(0.059)/(2)log.(1)/([H^(o+)])`
`=0.699-0.059pH`
`=0.699-0.059xx3.5`
`E_(cell)=0.4929-0.327=0.1659`