One event in a high school track meet is the 400 meter run. if the runners of the 400 meter event start and end at the same location, what is their displacement?
a) 0 meters
b) 200 meters
c) 400 meters
d) 800 meters

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.

the answer is a and have a great day