This is the periodic table of the elements. Javier's teacher gives him four cards, each displaying information about an element, and asks him to put them in order of reactivity. The elements are carbon (C), helium (He), magnesium (Mg), and potassium (K). Javier arranges the elements in order from most reactive to least reactive, as shown in the diagram. Is Javier's arrangement correct? Why or why not?

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.