Which statement most accurately describes a chemical equation? a. in a chemical reaction, the mass of the energy change must be equal to the energy used
b. in a chemical reaction, the mass of the products must equal the mass of the reactants
c. in a chemical reaction, the mass of each product must be the same
d. in a chemical reaction, the combined mass of the container the substances is always equal

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.