The part of the experiment against which results are compared is
independent variable
dependent variable
control
constant
hypothesis

Control

Explanation:

The control is the variable that you don't change. Like, imagine you're doing an experiment and are trying to figure out how much of a faster growth rate occurs with fertilized plants. You will compare the fertilized plant to the unfertilized one, which is the control, to see the difference the fertilizer made.

Hope this helped :)

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.