Which substance has particles that are farther apart as a solid than they are as a liquid? This explains why ...
A. Neon glows when energized with electricity.
B. Water expands when it freezes.
C. Argon is a gas at normal temperature and pressure.
D. Oxygen can be condensed into a liquid at very cold temperatures.

answer is: c. the experiment shows that the red substance experienced a chemical change.

this is chemical change (chemical reaction), because two new substances are formed (metalig liquid and gas), the atoms are rearranged and the reaction is followed by an energy change.

this is example of chemical decomposition.

chemical decomposition (analysis) is the separation of a single chemical compound into its two or more elemental parts or to simpler compounds.  

chemical decomposition is opposite of chemical synthesis.