The following reaction occur between S2​O32−​ and Cr2​O72−​ :26H++3 S2​O32−​+4Cr2​O72−​⟶6SO42−​+8Cr3++13H2​OChange in oxidation number of Cr2​O72−​ per formula unit is 6 (it is always fixed for Cr2​O72−​ ).Hence, equivalent weight of K2​Cr2​O7​=6 Molecular weight ​