Answer:
I believe the answer is "b". "During the experiment, the scientist has only one element, or variable, that is changed to test the hypothesis."
Explanation:
I remember from last year but I'm not totally sure. Good luck!
15mL because if it started as 20 mL and went to 35mL when u put in pyrite, the pyrite takes up 15mL
An endothermic reaction is when the energy is absorbed, while an exothermic reaction releases energy.