Question 3
Why do both curves level off at 4.8 g?
The right answer is the one marked above.
Because the two starting masses of CaCO3 were equal, so the amount that can be used up is equal too. Once all the CaCO3 is gone there is nothing left to use up.
A curve levelling off means the reaction has finished. Both stopping at the same height is the evidence that changing the rate does not change the amount of product.