What does the symbolupper deltain a chemical equation mean?

Triangle as a chemical symbol is actually a Greek alphabet 'delta'(upper case).In a chemical reaction it delta is just used as a symbol for 'heat'.

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.

a chemical change results in a new substance being formed; whereas a physical change will result in a different state of matter

explanation: