The valency factor of I2 when, (i) it is formed by the reaction of potassium iodide and potassium iodate in acid medium and (ii) when it reacts with hypo, are respectively

i  IO3−  +  I−  +  H+ →   I2+H2OI2 can be said to have undergone disproportionation.i  IO3−  +  I−  +  H+ →   I2+H2O∴    v.f.   of  I2  for  oxidation, n1=25−0=10and    v.f. of I2  for reduction,  n2=20−−1=2∴    v.f.   of  I2   overall   n1n2n1+n2=10 ×  210 +  2=53ii   I2+2Na2S2O3 →   Na2S4O6 +2NaII2+2e− →   2I− ⇒   v.f.  =2