1 equivalent of KMnO4 oxidizes 1 equivalent of ferrous sulfate to ferric sulphate.
50 ml of 0.1 N KMnO4 corresponds to 501000×0.1=0.005 moles of KMnO4.
It is also equal to the number of moles of ferrous sulphate.
The molar concentration of Fe2+ ions is 0.005100×1000=0.05 M.
The concentration of Fe2+is 55.8×0.05=2.8gL−1 =3gL−1.