What is a stock solution?

• A. A solution used directly in experiments at full strength.
• B. A solution with unknown concentration.
• C. A more concentrated solution that will be diluted to a lower concentration for actual use.
• D. A solvent with zero solute.

Answer: (C)

A stock solution is a concentrated, known‑concentration solution kept ready so you can make many working solutions by diluting with solvent to the desired final concentrations. The idea is to have a reproducible, labeled concentrate that lets you prepare exact amounts of other solutions quickly and accurately.

For example, if you need 1 liter of a 1 M solution and you have a 10 M stock, you would take 100 mL of the stock and add solvent until you reach 1 liter. This uses the dilution principle C1V1 = C2V2 to achieve the needed concentration precisely.

Using a solution at full strength is not the typical purpose of a stock, since stocks are meant to be diluted. A stock has a known, not unknown, concentration, and a pure solvent has zero solute, so those options don’t describe the practical role of a stock solution.