Answer
(a) The figures (b) and (d) represent pure solutions.
(b) The drawings (a) and (c) represent mixtures.
(c) The figures (b) and (d) illustrate the law of multiple proportions.
Work Step by Step
(a)
Pure solutions only have one type of molecule/atom/ion; since (b) only has the molecule with 1 blue sphere and 2 red spheres, it represents a pure solution. And since (d) has just 6 of the same atom, it is also a pure solution.
(b) Mixtures are solutions with two or more types of molecules/atoms/ions. (a) has red sphere atoms and blue sphere ones. (c) has red spheres molecules, and blue spheres ones, so they are both mixtures.
(c) The representations in (b) and (d) show that combined atoms from (a) and (c) obey the law of multiple proportions because they followed a fixed proportion, where the chemical reaction didn't involved fractional parts of atoms.