Concept:Indigo is an ancient vat dye characterized by a bis-indole conjugated ring system used globally for dyeing cotton yarns in denim production.
Formula / Reaction:$$\text{C}_{16}\text{H}_{10}\text{N}_2\text{O}_2 \quad (\text{Indigo})$$
Solution:- Indigo is insoluble in water in its colored keto form and must be reduced to water-soluble 'leuco-indigo' for fiber absorption.
- Subsequent atmospheric oxidation traps the insoluble indigo pigment inside the cotton fibers.
Why other options are incorrect:- Methyl orange: A synthetic monoazo dye used primarily as an acid-base indicator.
- Malachite green: A synthetic triarylmethane dye used for silk, wool, and as an antimicrobial agent.
- Basic fuchsin: A synthetic triphenylmethane dye used in biological staining and textile dyeing.
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