The equivalent mass of ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7$ when it acts as an oxidizing agent in an acidic medium is equal to

The molecular weight of a solute divided by its valence is used to calculate the equivalent weight of a solution.
$2{\mathrm{K}}^{+}+ 2{\mathrm{Cr}}^{3+}+7{\mathrm{H}}_2\mathrm{O}\to {\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7 +14{\mathrm{H}}^{+}+6{\mathrm{e}}^{-}$
Six electrons are involved in the chemical process, hence 6 is the chemical equivalent.
Equivalent mass
Molecular weight divided by chemical equivalent yields equivalent weight (Z).
= $\frac{\mathrm{M}}{6}$