Ben and jerry were testing powders in science lab. first they put the powder in a zip lock bag. next they added some water. the powder fizzed and bubbled; soon it disappeared. when the bubbling stopped the bag contained a clear liquid and a lot of gas. what is the most obvious sign of a chemical change in this reaction?

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.