**Assertion (A):** Kjeldahl's method cannot be used to estimate nitrogen in pyridine. **Reason (R):* — Qualitative and Quantitative Analysis Chemistry Question

💡 Solution & Explanation

Kjeldahl's method requires the organic nitrogen to be quantitatively reduced to the ammonium ion ($NH_4^+$) upon heating with concentrated $H_2SO_4$. Nitrogen tightly bound within an aromatic heterocyclic ring (like pyridine or quinoline) resists this degradation.