1A: The legs can be a adjusted, as well as the sand can be swapped out. It’s a very good design for running multiple tests.
1B: He could add books or something under the front or back legs in order to increase/decrease the incline, therefore imitating the hypothesis.
1C: He can change out the sand grains to finer ones, or coarser ones, and record his results of each test.
2: If he sets the model at a steep incline and tests it with coarse sand and fine sand, seeing which one makes a narrower, deeper hole.
Answer: 0.055 moles of 
are produced by the reaction of 0.055 mol of ammonium perchlorate.
Explanation:
The balanced chemical reaction for decomposition of ammonium perchlorate is:
According to stoichiometry :
2 moles of 
produce = 2 moles of
Thus 0.055 moles of will produce =
of
Thus 0.055 moles of are produced by the reaction of 0.055mol of ammonium perchlorate.
Hopefully this will help you my friend.
