2. Many calculations in chemistry will involve certain symbols, such as the symbol triangle or delta What does this symbol stand for or mean?
A. "The total"
B. "The change in"
C. "The unit"
D. "The formula"

B. "The change in"

I saw that symbol a lot in chemistry and physics so I immediately recognized it.

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.