Which of the following is/are considered as primary standard(s) in volumetric analysis? — Redox Reactions and Volumetric Analysis Chemistry Question

💡 Solution & Explanation

**(A/C)** Primary standards must be available in high purity, be stable in air, and have high molecular weight. $K_2Cr_2O_7$ and Oxalic acid dihydrate meet these criteria. <br>**(B)** $KMnO_4$ is not a primary standard because it is difficult to obtain in pure form and its concentration changes over time due to slow decomposition. <br>**(D)** Hypo ($Na_2S_2O_3$) is efflorescent and its concentration changes.