Hydrogen peroxide acts both as an oxidising and as reducing agent depending upon the nature of the reacting species . In which of the following cases $\;H_{2}O_{2}\;$ acts as a reducing agent in acid medium ?

Question

$(a)\;MnO_{4}^{-}\qquad(b)\;Cr_{2}O_{7}^{2-}\qquad(c)\;SO_{3}^{2-}\qquad(d)\;KI$