Peroxodisulfate Ion Can Oxidize Iodide Ions to Iodine According to the Balanced

Peroxodisulfate ion can oxidize iodide ions to iodine according to the balanced equation S₂O₈^2- + 2I ^-  2SO₄^2- + I₂.
The reaction is catalyzed by certain chemical species. Identify the catalyst in the following mechanism:
Step 1: Fe³⁺ + 2I ^-  Fe²⁺ + I₂
step 2: S₂O₈^2- + Fe²⁺  2SO₄^2- + Fe³⁺

A) Fe³⁺
B) I ^-
C) S₂O₈^2-
D) Fe²⁺
E) SO₄^2-