The correct option is A 0.28
Fe3+=x
Fe2+=0.93−x
Using charge balance
Fe0.9S1.0 =Charge on neutral compound =0
3×x2×(0.93−x)+2×1=0
Charge on Fe0.9
(Fe2+& Fe3+)
⇒3x+2(0.9−x)=2×2
3x+1.8−2x=2
x=2−1.8
x=0.2
Thus the no. of Fe+2 ion =0.93−x
=0.93−0.2
=0.73
Ratio Fe3+Fe2+=0.20.73
=0.28