Challenge Questions: Balance the equations below.
___ NaNO3 + ___ PbO → ___ Pb(NO3)2 + ___ Na2O
___ Ca3P2 + ___ H2O → ___Ca(OH)2 + ___ PH3
___Fe2O3 + ___ CO → ___Fe + ___ CO2
___NH3 + ___ O2 → ___ NO2 + ___ H2O
___FeS + ___O2 → ___Fe2O3 + ___SO2
___ C3H6O2 + ___ O2 → ___ CO2 + ___ H2O

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.