Answer and Explanation:
Using Gauss's law,
If r>a
then charge enclosed in all the three cases is same as Q.
So Electric field for all three is same.
So {1,1,1}.
(b) r<a,
Charge enclosed in case of shell is zero since all charge is present on the surface. So E = 0.
Charge enclosed by incase of point charge is Q.
Charge enclosed in case of sphere is Qr3/a3 which is less than Q.
So ranking {2,3,1}