What is the smallest particle of a compound that retains all of the properties of that compound

Why do cells appear different in distilled water than they do in 10% salt water?

The time that is taken by neptune once around the sun is called

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