Concept:Vat dyes are characterized by insoluble keto groups that undergo reversible reduction to alkali-soluble leuco compounds during textile dyeing.
Formula / Reaction:$$\text{Dye}=\text{O} \xrightarrow{[\text{H}]} \text{Dye}-\text{OH (Leuco form)} \xrightarrow{[\text{O}]} \text{Dye}=\text{O (Insoluble pigment)}$$
Solution:- This two-step application grants vat dyes exceptional wash- and light-fastness because the final oxidized dye is insoluble in water.
Why other options are incorrect:- Direct dyes: Water-soluble anionic compounds that adsorb directly to cellulose via hydrogen bonding.
- Acid dyes: Water-soluble sulfonated dyes applied to protein fibers (wool, silk) from acidic baths.
- Basic dyes: Cationic dyes that bind electrostatically to anionic sites on acrylic or protein fibers.
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