Which of the following statements are correct?
(i) Solution culture/hydroponics contains all essential minerals except one, the usefulness of which is to be determined.
(ii) Na, Si, Co and selenium are beneficial element required by higher plants.
(iii) Zn is the activator of nitrogenases while Mo is the activator of alcohol dehydrogenase.
(iv) Zn is needed for auxin synthesis.