What most likely accounts for the difference between curve A and curve B on the energy diagram?
A. The reaction described by curve B is occurring with a catalyst.
B. The reaction described by curve B is at a different temperature.
C. The reaction described by curve B is under greater pressure.
D. The reaction described by curve B has higher reactant
concentrations.

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.

idk what the question is about