Which of the following statements relating to a solution is NOT correct?

• A. A solution is a homogeneous mixture of two or more substances.
• B. The solute is always a solid and the solvent is always a liquid.
• C. Solutions can exist in gaseous, liquid, or solid phases.
• D. The concentration of a solution can be expressed in molarity (mol/L).

Answer: (B)

Verified step by step guidance

1. Step 1: Understand the definition of a solution. A solution is a homogeneous mixture of two or more substances, meaning the composition is uniform throughout the mixture.
2. Step 2: Recognize that the solute is the substance being dissolved, and the solvent is the substance doing the dissolving. Both solute and solvent can be in various phases (solid, liquid, or gas), not limited to solute as solid and solvent as liquid.
3. Step 3: Recall that solutions can exist in different phases: gaseous (e.g., air), liquid (e.g., saltwater), and solid (e.g., metal alloys). This means solutions are not restricted to liquid solvents only.
4. Step 4: Understand concentration units such as molarity, which is defined as moles of solute per liter of solution (\(\text{Molarity} = \frac{\text{moles of solute}}{\text{liters of solution}}\)). This is a common way to express solution concentration.
5. Step 5: Identify the incorrect statement by comparing each option to these principles. The statement claiming 'The solute is always a solid and the solvent is always a liquid' is incorrect because solutes and solvents can be in any phase.