Is Helium a compound, element, or. mixture

Which sentence about particles in matter is true? a. atoms are present in solids and liquids but not in gases. b. the particles of matter are in constant motion. c. the same kinds of atoms are found in different elements. d. when a solid changes to a liquid, the sizes of the particles change.

The twister and runaway train are two coasters at the same amusement park. both coasters start at the same height. the coaster for the twister is twice the mass of the coaster for the runaway train. which roller coaster has greater gravitational potential energy at the start of the ride?

Water is initially present in a state where its molecules are far apart. during a change of state, its molecules slow down. which change of state has most likely taken place? from a gas to a liquid from a liquid to a gas from a solid to a liquid from a gas to a plasma