Concentration describes the amount of solute per unit volume or mass in a solution. Which option expresses this concept most accurately?

• A. The mass of solute per unit volume or mass of a solvent.
• B. The amount of solute per unit volume or mass in a solution.
• C. The temperature dependence of solubility.
• D. The ratio of solute to solvent.

Answer: (B)

Concentration is about how much solute is present in a given amount of solution. Saying it as the amount of solute per unit volume or per unit mass in a solution covers the common and practical ways we quantify it, such as moles per liter (molarity) or grams per liter (mass concentration). It also stays general enough to include other measures that relate solute to the solution itself.

Using the mass of solute per unit volume or mass of a solvent would mislead, because concentration is defined with reference to the solution as a whole, not just the solvent. The idea of a simple ratio of solute to solvent doesn’t consistently capture how concentration is measured and compared in practice. And focusing on how solubility changes with temperature or on solute-to-solvent ratios misses the defining idea that concentration describes how much solute exists in a given amount of solution.