Standard electrode potentials are
`Fe^(2+)//Fe, E^(@) = -0.44 V`
`Fe^(3+)//Fe^(2+), E^(@) = +0.77 V`
If `Fe^(3+), Fe^(2+)`, and Fe block are kept together, then

Options

A. `Fe^(3+)` increases
B. `Fe^(3+)` decreases
C. `Fe^(2+)|Fe^(3+)` remains unchanged
D. `Fe^(2+)` decreased

Answer

B

Explanation

For e.m.f. to be positive , the following half cell reactions will occur :
`Fe to Fe^(2+) + 2e^(-) " " E^(@) = +0.44 V`
`2 Fe^(3+) + 2e^(-) to 2 Fe^(2+) " " E^(@) = +0.77 V `
Overall reaction :
`Fe + 2 Fe^(3+) to 3 Fe^(2+) " " E^(@) = +1.21 V `
`therefore Fe^(3+)` will decrease .