petroleum refining involves fractional distillation. which physical property allows the different fractions to be separated?

How is the atomic number of a nucleus changed by alpha decay

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium

How does science use models to gain a better understanding of concepts?