The Peroxydisulfate Ion (S₂O₈^2-)reacts with the Iodide Ion in Aqueous

The peroxydisulfate ion (S₂O₈^2-) reacts with the iodide ion in aqueous solution via the reaction:
S₂O₈^2- (aq) + 3I^- → 2SO₄ (aq) + I₃^- (aq)
An aqueous solution containing 0.050 M of S₂O₈^2- ion and 0.072 M of I^- is prepared, and the progress of the reaction followed by measuring [I^-]. The data obtained is given in the table below.
-The average rate of disappearance of I^- in the initial 400.0 s is ________ M/s.

A) 6.00
B) 3.8 × 10^-5
C) 1.4 × 10^-4
D) 2.7 × 10⁴
E) 3.2 × 10^-4