The balanced ionic equation for the reaction is,
MnO−4 + 5Fe2+ + 8H+→Mn2+ + 5Fe3+ + 4H2O
From the balanced ionic equation, it is evident that 1 mole of KMnO4 require 5 moles of FeSO4, applying law of chemical equivalence, we get
M1V1n1(KMnO4)=M2V2n2(FeSO4)
(where n is n-factor)
so, 18×V1×5=14×25×1
V1=10 cm3
or V1=10 mL