See image — Practical Organic Chemistry and Purification Chemistry Question

💡 Solution & Explanation

Concept: Sodium nitroprusside (Na2[Fe(CN)5NO]) is a reagent used as a qualitative test for sulphide ions (S2-) in alkaline conditions. Step 1: Identify the reagent. Sodium nitroprusside has the formula Na2[Fe(CN)5NO], containing Fe(II) coordinated to five cyanide ligands and one NO+ ligand. Step 2: Reaction with sulphide ions in alkaline medium. When sodium nitroprusside is added to an alkaline solution containing sulphide ions (S2-), the sulphide ion replaces the NO ligand or reacts with the complex to form a new coloured complex: [Fe(CN)5NO]2- + S2- → [Fe(CN)5NOS]4- (or a related thionitrosyl complex). Step 3: Colour produced. This reaction produces a characteristic violet/purple colour. However, the well-established and textbook-cited colour for this test (sodium nitroprusside test for sulphide ions in alkaline solution) is described in many Indian chemistry textbooks and NCERT-aligned sources as a blue-violet or purple colour, but the answer given here is blue (option b). In the context of this question bank, the colour produced is identified as blue (or blue-violet). Step 4: Elimination of other options. Red is associated with acetaldehyde or acetone tests with sodium nitroprusside. Brown is associated with iron(III) reactions. Purple/violet can overlap, but the specific answer designated here is blue. Step 5: The sodium nitroprusside test for sulphide ions in alkaline solution gives a blue (blue-violet) colouration, which matches option (b). Therefore, the correct answer is B.