What is the process by which compounds a break down into a simpler substance is called

There can be a number of chemical processes by which a compounds can be broken down into simpler substances. The most common and wide-spread of such processes is Catabolism. Along with anabolism, catabolism make up the metabolism process for living organisms.

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.

0.88m hope i am correct : )