What describes a standard solution?

• A. A mixture of equal parts solute and solvent.
• B. A solution in which the exact concentration of a chemical is known.
• C. A solvent with no solute.
• D. A solution with unknown concentration used for titration.

Answer: (B)

A standard solution is a solution whose concentration is known exactly. This precise, known concentration makes it possible to calibrate instruments, standardize other solutions, and perform accurate quantitative measurements such as titrations. When you prepare a standard, you measure the amount of solute and the volume of solvent very carefully to achieve a specific, reproducible concentration that you can rely on for calculations.

The other descriptions don’t fit standard solutions. A mixture with equal parts solute and solvent implies a fixed ratio but not necessarily a precisely known concentration, so it isn’t guaranteed to be a standard. A solvent with no solute is not a solution at all. A solution with unknown concentration used for titration would be a sample whose concentration you don’t know, not a standard you can rely on for calibration or calculation.