Which of the following substances are correctly matched with their classification as standard soluti — Redox Reactions and Volumetric Analysis Chemistry Question

💡 Solution & Explanation

Primary standards must be stable, highly pure, non-hygroscopic, and directly weighable (e.g., $K_2Cr_2O_7$, Oxalic acid, Mohr's salt). Secondary standards require standardization against a primary standard before use because they are unstable or hygroscopic (e.g., $NaOH$ absorbs moisture and $CO_2$; $KMnO_4$ is light-sensitive and decomposes).