Answer:
Maria has not taken the reading for densities of the two solutions individually
Step-by-step explanation:
Maria has not taken the reading for densities of the two solutions individually. Since Maria is aiming to compare the result of density of each individual solution with the density of the combined solution, she must have the reading for individual solution densities.
However, all other test proceedings are correct.
Here, the densities of individual solution shall act as control group which shall be compared with the experimental group i.e the density of combined solution.