Concept:Direct dyes are long, planar, conjugated organic molecules containing polar groups (such as \(-\text{OH}\) and \(-\text{SO}_3\text{Na}\)) that bind to cellulose via hydrogen bonding and van der Waals forces without a mordant.
Formula / Reaction:$$\text{Cellulose}-\text{OH} \cdots \text{H}-\text{O}-\text{Dye} \quad (\text{Intermolecular Hydrogen Bonding})$$
Solution:- Direct dyes have high affinity (substantivity) for cotton and viscose rayon due to their linear planar geometry that aligns parallel to cellulose polymer chains.
Why other options are incorrect:- Triarylmethane dye: Basic cationic dyes with triphenylmethane skeletons used mainly for paper and acrylics.
- Anthraquinone vat dye: Water-insoluble polycyclic pigments requiring chemical reduction.
- Disperse dye: Non-ionic, water-insoluble dyes for synthetic hydrophobic fibers.
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