Proteins Containing a Certain Functional Group (Identified as RSH)can Be $\to$

Proteins containing a certain functional group (identified as RSH) can be titrated with triiodide ion to produce another functional group (identified as RSSR) .The reaction equation is given below.What is oxidized and what is reduced in this reaction? 2 RSH(aq) + I₃^-(aq) $\to$ 3 I^-(aq) + RSSR(aq) + 2 H⁺(aq)

A) RSH is oxidized,I₃^- is reduced.
B) RSH is reduced,I is oxidized.
C) Both RSH and I are oxidized.
D) Both RSH and I are reduced.
E) This reaction is not oxidation-reduction.