What is it called in a chemical compound name when there is....?

What is it called in a chemical compound name when there is a) roman numerals in it e.g. (II) and (IV)? and b) a 1 or a 2 or a 1 then a comma then a 25 e.g 2-ethylhexyl acrylat or 1,25-dihydroxycholecalciferol ?