What is the atomic number?
pls help.

Which organism develops breathing organism develops breathing organs from pharyngeal arches? shark, spider, sea star, sea horse

The most common form of matter in the universe

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