Which of the following best explains why a solution is not considered a pure substance?

• A. A solution consists of molecules that are all identical.
• B. A solution contains two or more substances physically combined, not chemically bonded.
• C. A solution has a fixed composition and cannot be separated by physical means.
• D. A solution is made up of only one type of atom.

Answer: (B)

Verified step by step guidance

1. Understand the definition of a pure substance: a pure substance has a fixed composition and consists of only one type of particle, either atoms or molecules, chemically bonded together.
2. Recognize that a solution is a homogeneous mixture composed of two or more different substances physically combined, not chemically bonded.
3. Recall that because the components in a solution are physically combined, they can be separated by physical means such as filtration, evaporation, or distillation.
4. Note that a solution does not have a fixed composition; the ratio of solute to solvent can vary, unlike a pure substance which has a constant composition.
5. Conclude that a solution is not a pure substance because it contains multiple substances physically mixed, not chemically bonded, and can be separated by physical methods.