The reaction takes place when Na2S2O3 is standardised using K2Cr2O7 is as follows : 4Cr2O72−+3S2O33−+26H+⟶6SO42−+8Cr3++13H2O The oxidation state of chromium in K2Cr2O7 changes from +6 to +3. The net change in oxidation number per formula unit is 6 . ∴ Value of n - factor = 6 Equivalent weight, E =