Estimation of reducing substances by the use of standard I2, I2+2S2O32−⟶S4O62−+2I⊖is called

Iodometric Titration:These are the titrations in which free iodine is used as it is difficult to prepare the solution of iodine (volatile and less soluble in water), it is dissolved in KI solution. This solution is first standardized before using with the standard solution of substance such as sulphite, thiosulphate, arsenite  etc. are estimated.