Which of the following statements are correct with respect to benzene?
(i) It forms triozonide with O$_3$.
(ii) It is non-planar.
(iii) It forms only one monosubstituted product with CH$_3$COCl in the presence of anhyd. AlCl$_3$.
(iv) It forms hexachlorobenzene on heating with Cl$_2$ under photochemical condition.