The number of moles of KMnO₄ that will be needed to react completely with one mole of ferrous oxalate in acidic solution is

${\mathrm{KMnO}}_4+{\mathrm{FeC}}_2{\mathrm{O}}_4 +{\mathrm{H}}^{+}\to \mathrm{M}{\mathrm{n}}^{2+}+\mathrm{F}{\mathrm{e}}^{3+}+ 2{\mathrm{CO}}_2$

Now we can say that,

Here KMnO₄ = 5 electrons change in oxidation state

ferrous oxalate in acidic solution = 3 electrons

while reaction exchange of electrons takes place..........so

3 moles of KMnO₄ = 5 moles of FeC₂O₄

5 moles of FeC₂O₄ = 3 moles of KMnO₄

so 1 mole of FeC₂O₄ = 3/5 moles of KMnO₄

hence 3/5 moles of KMnO₄ of KMnO₄ will be needed to react completely with one mole of ferrous oxalate in acidic solution