For a molecule to be aromatic following conditions should be followed-

1) Molecule should be planar.

2) Electrons should be completely delocalized.

3) Huckel’s rule- it should have (4n+2) electrons in ring where n= 0,1,2...

(i) Planar, no. of electrons = 2, 4n+2 = 2 => n=0 Therefore, ring is aromatic.

(ii) Since, ring is not planar therefore, it is non aromatic.

(iii) Planar, no. of electrons = 6, 4n+2 = 6 => n=1 Therefore, ring is aromatic.

(iv) Planar, no. of electrons = 4, 4n+2 = 4 => n=0.5 Therefore, ring is not aromatic.

Therefore, (i) and (iii) are aromatic structures.