CrO42− is a stronger oxidising agent as compared to MnO42−. Cr+6→[Ar]3dn4sn which is stable. So, Cr reading loses its 6 electrons to attain stable noble gas and acting as oxidising agent but in Mn+6 [electronic configuration is [Ar] 3d′4su ] one electron is defficult to remove and acquire stable form. Hence, MnO4−is not oxidising agent but CrO4‌2− is good oxidising agent.