Acidified K2Cr2O7,CuSO4,H2O2,Cl2,O3,FeCl3 and HNO3 oxidise aq. iodide to iodine. Alkaline KMnO4 oxidise aq. iodide to IO−3.
Na2S2O3 is a strong reducing agent which on reaction with I2 produces I−.
Na2S2O3+I2→2I−+Na2S4O6
Therefore, no reaction takes place between Na2S2O3 and iodide ion.
Hence, correct integer is (7).