since titanium ion is tetrapositive , while the iron atom is dipositive, every Fe2+ ions will be replaced by 1 Ti4+ ion. Thus, 0.4 out of 0.9 mole of Fe2+ will be replaced.

Thus moles of Fe2+ left = 0.5 mol

molarity of Fe2+ = 0.5M (since it is dissolved in 1 L H2O)

nnormality of Fe2+ for the reaction

 

Fe2+ --> Fe3+ + e-

 

is 0.5N

Thus,

the volume of KMnO4 required ccan be calculated(I am not calculating it as the strength of KMnO4 sol. has not been properly indicated in the question.)