-The Concentration of an Aqueous Solution of I₃⁻ Can Be

-The concentration of an aqueous solution of I₃⁻ can be determined by a redox titration with aqueous sodium thiosulfate,Na₂S₂O₃: 2 S₂O₃^2- (aq) + I₃⁻ (aq) + → S₄O₆^2- (aq) + 3 I⁻ (aq)
Assume that the black spheres in the buret represent S₂O₃^2- ions,the gray spheres in the flask represent I₃^- ions,the concentration of the S₂O₃^2- ions in the buret is 0.120 M,and the volumes in the buret and the flask are identical.What is the concentration of the I₃^- in the flask,and what fraction of the S₂O₃^2- solution in the buret must be added to the flask to react with all the I₃^- ions?

A) 0.0400 M I₃^-;1/3 of the S₂O₃^2- must be added.
B) 0.0400 M I₃^-;2/3 of the S₂O₃^2- must be added.
C) 0.0600 M I₃^-;1/3 of the S₂O₃^2- must be added.
D) 0.0600 M I₃^-;2/3 of the S₂O₃^2- must be added.