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^(+++)]` decreases
B. `[Fe^(+++)]` increases
C. `[Fe^(++).Fe^(+++)]` remains unchanged
D. `[Fe^(++)]` decreases

Answer

A

Explanation

`Fe^(2+)//Fe` acts as anode, `Fe^(+++)//Fe` acts as cathode.
`thereforeFerarrFe^(2+)+2e^(-)("Anode")`
`and ((Fe^(3+)+e^(-)rarrFe^(2+))xx2("Cathode"))/(Fe+2Fe^(3+)rarr3Fe^(2+))`
Thus if `Fe^(2+),Fe^(3+)` and Fe block are kept together `Fe^(3+)` get reduced to `Fe^(++)` i.e., concentration of `Fe^(3+)` decreases.