Consider the Equilibrium That Exists Between Fe²⁺ and Fe³⁺ Ions

Consider the equilibrium that exists between Fe²⁺ and Fe³⁺ ions in solution.The extra electron originally on one Fe²⁺ ion can be transferred to an Fe³⁺ ion.This amounts to no net reaction because iron(II) becomes iron(III) and iron(III) becomes iron(II) .Which below about this equilibrium is true?

A) There is no activation energy for this reaction.
B) K = 1.
C) K =0.
D) There is no net reaction, so there is no value for K.
E) The concentrations of iron(II) and iron(III) change because of the electron transfer.