Me some coal emits sulfur when it is burned. why is this a problem? a. sulfur is black and coats surfaces with black dust. b. sulfur forms sulfur dioxide, which acts as an air pollutant. c. sulfur produces heat so it needs to remain in the coal. d. sulfur increases the greenhouse effect.

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.