How many of the following statements are true ?
(i)Chromate ion is square planar
(ii) Green manganate  ion is diamagnetic
(iii) Sodium dichromate can be prepared from sodium chromate.
(iv) Purple ${\text{KMnO}}_{\text{4}}$ disproportionates in acidic medium and neutral  medium
(v) Ionic character of oxides decreases with increase in oxidation number of transition metal