Determine the oxidation number of following underlined elements:KI3

KI3:1+3(a)=0⇒a=−1/3Since KI3 is HI +I2; therefore, I has two oxidation numbers -1 and 0, respectively.However, oxidation number of I in KI3 is an average of two  values -l and 0.Therefore, average oxidation number = −1+2(0)3=−13