Which scenario represents a physical change in matter?

The boiling of a refrigerant exemplifies a physical change in matter because during this process, the refrigerant transitions from a liquid state to a gaseous state without altering its chemical composition. When a substance undergoes a physical change, it retains its identity, and its molecular structure remains intact.

This specific action, boiling, involves the absorption of heat which increases the kinetic energy of the molecules, causing them to move apart and change from liquid to vapor. Regardless of this phase shift, the refrigerant can still return to its original liquid form if the temperature is lowered, demonstrating that no new substance has formed.

In contrast, the other scenarios involve chemical changes where substances undergo transformations to create entirely new materials with different properties. The reaction of sodium with chlorine forms sodium chloride (table salt), burning of coal converts it into gases, ash, and other products, and rusting of steel indicates a reaction between iron and oxygen to produce iron oxide. These processes result in substances that are chemically different from their reactants, which clearly distinguishes them from the physical change represented by boiling.