See image — Practical Organic Chemistry and Purification Chemistry Question

💡 Solution & Explanation

Step 1 - Understand the problem: We need to differentiate four compounds - m-nitrophenol (weak acid), m-nitrobenzoic acid (stronger acid), m-nitroaniline (base), and m-dinitrobenzene (neutral) - using three reagents in decreasing order of their differentiating ability. Step 2 - Assess acidity/basicity of each compound: - m-nitrobenzoic acid: strong enough acid to react with NaHCO3 (pKa ~3.5), reacts with both NaOH and NaHCO3 - m-nitrophenol: weak acid (pKa ~8.4), reacts with NaOH but NOT with NaHCO3 - m-nitroaniline: base, reacts with HCl (forms ammonium salt) - m-dinitrobenzene: neutral, does not react with NaOH, NaHCO3, or HCl Step 3 - Determine the correct order of reagents: - First reagent NaHCO3: Only m-nitrobenzoic acid reacts (gives CO2 effervescence). This separates the carboxylic acid from the rest. - Second reagent NaOH: m-nitrophenol reacts (dissolves in NaOH) but m-nitroaniline and m-dinitrobenzene do not. This separates the phenol. - Third reagent HCl: m-nitroaniline reacts with HCl (basic amine forms salt and dissolves). m-dinitrobenzene does not react. This separates the amine from the neutral compound. Step 4 - Match to options: The order NaHCO3, NaOH, HCl corresponds to option (c). Step 5 - Why other options fail: - Option (a) NaOH first would react with both the carboxylic acid and phenol simultaneously, not distinguishing them cleanly in decreasing order of reactivity. - Option (b) HCl first only identifies the amine, but carboxylic acid and phenol (stronger acids) should be identified before the base. - Option (d) NaOH first again does not use the most selective (NaHCO3) reagent first. The correct decreasing order of reagent strength/selectivity for differentiation is: NaHCO3 (reacts only with strongest acid - carboxylic acid), then NaOH (reacts with weaker acid - phenol), then HCl (reacts with base - aniline), leaving the neutral compound unreacted throughout. Therefore, the correct answer is C.