The standard reduction potentials for `Zn^(2+)//Zn,Ni^(2+)//Ni`and `Fe^(2+)//Fe` are -0.76,-0.23 and -0.44V respectively. The reaction `X+Y^(2+)to X^(2)+Y` will be spontaneous when :

Options

A. `X=Zn,Y=Ni`
B. `X=Ni,Y=Fe`
C. `X=Ni,Y=Zn`
D. `X=Fe,Y=Zn`

Answer

A

Explanation

The reaction `X+Y^(2+)toX^(2+)+Y` will be spontaneous if `E_(cell)^(@)` is +ve.
(a) `Zn+Ni^(2+)toZn^(2+)+Ni`,
`E_(cell)^(@)=E_(Ni^(2+)//Ni)^(@)-E_(Zn^(2+)//Zn)^(@)=-0.23-(-0.76)V`
(b) `Ni+Fe^(2+)toNi^(2+)+Fe,E_(cell)^(@)=E_(Fe^(2+)//Fe)^(@)-E_(Ni^(2+)//Ni)^(@)=-0.44-(-0.23)V`
`=-0.21V`
(c) `Ni+Zn^(2+)toNi^(2+)+Zn,E_(cell)^(@)=-0.53V` from (a)
(d) `Fe+Zn^(2+)toFe^(2+)+Zn,E_(cell)^(@)=E_(Zn^(2+)//Zn)^(@)=E_(Fe^(2+)//Fe)^(@)=-076-(-0.44)V=-0.32V`