What should you NOT do when trying to put out a grease fire?
A. cover the flames
B. add cold water
C. add baking soda
D. use an "ABC" fire extinguisher

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.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)

you need to have a picture of the atom that way we can answer it

pv=nrt

explanation: