When an electron falls from an excited state to ground state, is energy released or absorbed?

The diagram shows the relationship between scientific disciplines. the names of some scientific disciplines have been removed from the boxes. which scientific discipline belongs in the blue box? a. physics b. biology c. chemistry d. metallurgy

Anitrogen atom and an oxygen atom combine chemically to form nitric oxide. what is nitric oxide?

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