The correct option is C M/6
Reaction of K2Cr2O7 in acidic condition,
K2Cr2O7+14H++6e−→2K++2Cr3++7H2O
Here 2 atom of Cr reduced from +6 oxidation to +3 oxidation state. Hence 6 e− is involved in the redox reaction.
Equivalent mass of K2Cr2O7=Molecular massnumber of electrons involved in the reaction
Here, Molecular mass = M
Hence,
Equivalent mass of K2Cr2O7=M6