12. Describe an open system

Check the correct box to describe the periodic trends in electronegativity. electronegativity across a period: decreases. increases. electronegativity down a group: decreases. increases.

Will mark brainliest how many electrons can be held in the energy level n = 4?

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