In a car cylinder, a piston moves up and down inside a cylinder, causing the substance inside to expand and contract. which type of substance could be inside the cylinder?
gas only
liquid only
liquid or solid only
gas, liquid, or solid

The characteristics of two different types of reactions are shown below: reaction a: electrons are gained by the atoms of an element. reaction b: protons are lost by the atom of an element. which statement is true about the atoms of the elements that participate in the two reactions? their identity changes in both reaction a and reaction b. their identity changes in reaction a but not in reaction b. their identity changes in reaction b but not in reaction a. their identity remains the same in both reaction a and reaction b.