What holds the ions together in galena

Ionic bonds hold atoms together using the electrostatic charge between their positive and negative ions. These ions are formed when electrons are transferred between atoms, the net loss or gain determining if the ion is positive, called a cation, or negative, an anion.

Explanation:

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.