The n-factor for Potassium dichromate acting as oxidant in acidic medium is:

In the acidic medium , Potassium dichromate get reduced to Chromic ion, hence the change in   oxidation state per molecule of potassium dichromate is ‘6’.
In acidic medium,  ${\mathrm{K}}_2{\mathrm{Cr}}_2{\mathrm{O}}_7\to 2{\mathrm{Cr}}^{+3}$
Hence, n – factor = 6