What's the name of the model that democritus and leucippus created?

Why do sodium and neon have vastly different chemical and physical properties despite having similar atomic masses?

What volume of a 2.00 m stock solution of naoh is needed to prepare 150. ml of 0.40 m solution?

Nebulae are enormous clouds in outer space. they are made mostly of hydrogen gas, helium gas, and dust. some nebulae glow brightly, while others do not. the stars that people see are huge, bright balls of glowing gas. they are made mostly of hydrogen and helium. which statement correctly describes other ways in which nebulae and stars are different? a. stars can form inside a nebula but a nebula can never be produced by any star. b. a star always has a higher density than a nebula. c. stars can never form inside a nebula but a nebula can be produced by any star. d. a nebula always has a higher density than a star.