the half-life of chromium-51 is 28 days. if the sample contained 510 grams, how much chromium would remain after 56 days

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