See image — Practical Organic Chemistry and Purification Chemistry Question

💡 Solution & Explanation

Concept: Kjeldahl's method involves digesting a nitrogen-containing organic compound with concentrated H2SO4 to convert nitrogen into ammonium sulfate. Various additives are used to improve the efficiency and speed of this digestion. Reasoning: In Kjeldahl's method, K2SO4 (potassium sulfate) is added to the digestion mixture to raise the boiling point of sulfuric acid. Pure concentrated H2SO4 boils at about 337°C, but when K2SO4 is dissolved in it, the boiling point is elevated significantly (up to ~400°C or higher). This higher temperature accelerates the digestion process, allowing complete conversion of organic nitrogen to ammonium sulfate more efficiently. Why other options fail: - (a) Oxidising agent: K2SO4 is not an oxidising agent in this context; H2SO4 itself acts as the oxidising agent. - (b) Catalytic agent: Catalysts used in Kjeldahl's method are typically CuSO4 or mercury compounds (or mixtures like selenium), not K2SO4. - (c) Hydrolysing agent: K2SO4 does not hydrolyse the organic compound; it is not a hydrolysing agent in this process. K2SO4 functions solely to elevate the boiling point of the acid mixture, thereby increasing the digestion temperature and speeding up the reaction. Therefore, the correct answer is D.