Heidi is a chocolate lover and eats chocolate daily. She has a bad break-out and her friend told her eating chocolate causes pimples. Heidi continues to eat
chocolate every day for 2 weeks and counts the number of pimples she has on
her face. The following 2 weeks she doesn't eat any chocolate and counts the
number of pimples on her face.
a. Independent Variable =
b. Dependent Variable =
C. Control =

a. the weeks she ate the chocolate

b. how many pimples were on her face

c. how much chocolate she ate

(I'm pretty sure A. is right but I might be wrong)

Explanation:

a. Independent Variable = time , starting number of pimples

b. Dependent Variable = the number of pimples

C. Control =  the chocolate quantity , 2 weeks for eating and 2 weeks for chocolate fasting " The think this time equalizing is a control factor "

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.