The standard reduction potential 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) rarr X^(2+) + Y` will be spontaneous when:

Options

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

Answer

C

Explanation

The element with high negative value of standard reduction potential is good reducing agent and can be easily oxidised . Therefore , X should have higher negative value of standard reduction potential than Y so that it will be oxidised to `X^(2+)` by reducing `Y^(2+)` to Y . Therefore ,
`X = Zn , Y = Ni`
`Zn + Ni^(2+) to Zn^(2+) + Ni`
or `E_(cell)^(@) = -0.23 - (-0.76) = + 0.53 V `
Since `E_(cell)^(@)` is +ve , the reaction is spontaneous .