<prompt> Most potent form of vitamin D is:1, 25- dihydroxy cholecalciferol7-dihydro cholecalciferol25-hydroxy cholecalciferolErgocalciferol Vit. D2  <response>: Vitamin D Ergocalciferol Vitamin D2 Formed from ergosterol and cholecalciferol vitamin D3 and are known as Pro-vitamins Vitamins D2and D3 are not biologically active. 25-OH- cholecalciferol Major storage and circulating form of vitamin D 1, 25 dihydroxycholecalciferol aka Calcitriol most biologically active form of vitamin D Vitamin D encompasses a group of sterols, which have a hormone-like function. Bioactive vitamin D or calcitriol is a steroid hormone that has long been known for its impoant role in regulating body levels of calcium and phosphorus, and in mineralization of bone. 