You drip a liquid substance onto a metal plate. You hear a hiss, and see a gas rising from the spot where the liquid touches the metal plate. What indicates a chemical reaction in this scenario?

the formation of a new gas

the hissing sound as the liquid touches the metal

the decrease in temperature as the liquid touches the metal

the liquid being in contact with a metal

What happens to isotopes that are unstable?

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.

Ajet plane is speeding down the runway during takeoff. air resistance is not negligible. identify the forces on the jet.