how do I do this I’m confused

What is the average rate of the reaction between 10 and 20 s?

How can parts of a solution be separated by chromatography?

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