Redox reaction: Iron(III) and Iodide ion
Iodine exists as a diatomic molecule. This reaction indicates how the iodide ion is converted into diiodine. Your reaction just indicates the electron transfer: you still need to balance the reaction.
You need an $\ce{I_2}$ molecule on the right hand side, which would need two iodide ions on the left hand side:
$$\ce{2 I- -&gt; I_2 + 2e-}$$
To accept two electrons, we would need two $\ce{Fe^3+}$ ions:
$$\ce{2 Fe^3+ + 2 e- -&gt; 2 Fe^2+}$$
Now we have a balanced reaction. All the electrons donated by iodine are accepted by iron. Adding up the two reactions and cancelling the electrons gives us:
$$\ce{2 Fe^3+ + 2I- -&gt; 2 Fe^2+ + I_2}$$