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) . What is true about this equilibrium?

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.