**(A):** is used as a primary standard in volumetric analysis. <br> **(R):** is stable in air, avail — Redox Reactions and Volumetric Analysis Chemistry Question

💡 Solution & Explanation

**Assertion:** A primary standard must be stable and pure. $K_2Cr_2O_7$ is a standard reagent for titrating $Fe^{2+}$. [4], [5] <br>**Reason:** These properties (purity, stability, and high mass to minimize weighing errors) are the defining criteria for a primary standard. [5]