Which term refers to a solution of known concentration used for standardization?

• A. Oxidation number
• B. Disproportionation
• C. Primary standard
• D. Electrolyte

Answer: (C)

In standardization work, you need a substance whose amount and concentration can be known with high accuracy. A primary standard is a substance of exceptional purity and stability that can be weighed precisely and dissolved to make a standard solution with a known concentration. This reliable reference solution is then used to calibrate or standardize other solutions and titrations. The other terms don’t describe something used to prepare or verify a known concentration: an oxidation number is just a way to track electron transfer, disproportionation is a redox reaction, and an electrolyte is a substance that conducts electricity when dissolved or molten. So the term that best fits a solution of known concentration used for standardization is primary standard.