The dye which is colourless in reduced form but becomes coloured by oxidizing agent is: (a) Mordant dye (b) Vat dye (c) Acid dye (d) None

Textile coloring is a process that adds vibrant colors to fabrics using various types of dyes. Each dye and coloring process has specific properties tailor-made to suit different materials and uses. For instance, vat dyes are unique because they need to undergo a chemical change to bond permanently with fabric fibers.

Initially, vat dyes are insoluble in water, which means they cannot directly dye fabric. To address this, they are chemically reduced to a soluble form, which allows them to penetrate the fibers of the textile. Once applied in this soluble form, they are exposed to air or a chemical oxidant to revert to their original, insoluble form. This process firmly locks the color into the fabric, ensuring a high level of wash and light fastness, making it ideal for coloring materials that will be washed frequently or exposed to harsh conditions.

The oxidation-reduction (redox) reactions play a crucial role in the function of vat dyes and many other coloring processes. In simple terms, reduction transforms the dye into a colorless, water-soluble form by adding electrons, making it capable of attaching to the fabric. Once inside the fabric, the reduced dye undergoes oxidation, which removes electrons, turning the dye back into its original, insoluble form and bringing out its full color.

This redox cycling explains why some dyes, like vat dyes, are colorless in their reduced state and vibrantly colored after oxidation. It's a bit like a color-changing magic trick, with chemistry as the magician. In educational terms, the redox principle exemplifies the practical application of reaction types studied in chemistry, showcasing the direct link between theoretical principles and real-world applications.

Dyes are fascinating chemicals that exhibit colors due to the presence of chromophores, which are molecular groups responsible for color. The chemistry behind dyes is complex and involves understanding how molecules absorb and reflect certain wavelengths of light. In vat dyes, the color change occurs through a redox reaction, which alters the structure of the chromophore.

Furthermore, a concept called resonance in dye molecules helps explain why the color appears so vivid. A structure in a molecule can resonate between two forms, and this delocalization of electrons is what allows specific wavelengths of light to be absorbed, imparting intense and vibrant colors to the material dyed.

Understanding the chemistry of dyes not only aids in better comprehending how colors are fixed onto textiles but also encourages the development of new, more sustainable dyes and coloring processes that might lessen environmental impacts.