The number of moles of and separately required to oxidise one mole of FeC₂O₄ each in acidic medium respectively

n-factor for MnO₄^- = 5 (MnO₄^- → Mn⁺²)
n-factor for Cr₂O₇^-2 = 6 (Cr₂O₇^-2 → Cr⁺³)
n-factor for FeC₂O₄ = 3 (Fe⁺² →Fe⁺³ & C₂O₄^-2 →CO₂)
 

n-factor
Criss cross
 

3moles of  MnO₄^- oxidizes 5 mole of FeC₂O₄
'X' mole of MnO₄^- oxidizes 1mole of FeC₂O₄
 

n-factor
Criss - cross method
3 moles of Cr₂O₇^-2 oxidizes 6 mole of FeC₂O₄
'X₂' mole of Cr₂O₇^-2 oxidizes 1 mole of FeC₂O₄