What is a common characteristic of a primary standard?

A primary standard is a substance that is used as a reference in a titration and is characterized by having a known and stable concentration. This stability is crucial because it ensures reproducibility and accuracy in analytical procedures. Primary standards are typically highly pure, with a known stoichiometry, allowing for precise calculations of concentration and molarity when performing reactions.

The requirement for a known concentration allows for accurate calibration of other substances and methods, making primary standards essential for quantitative analysis. Due to their purity and stability, these standards can be used to determine the concentration of other solutions, a vital aspect of analytical chemistry.

In contrast, options that imply low purity requirements, the necessity of being calibrated, or being limited to a liquid form do not align with the definition or characteristics of primary standards. Primary standards must be highly pure, can often be solid, and are utilized directly in quantitative analysis without requiring calibration against another standard.