Question

Select the odd pair

Options

• Optical brighteners - coloured dyes

• Aniline blue - water soluble

• Indigo blue - insoluble in water

• Ultra-marine blue - popular in households

Answer 1

Optical brighteners - coloured dyes

Explanation:

Optical brighteners are not colourful dyes; they are colourless substances that absorb UV radiation and release it as visible blue light, causing materials to look whiter and brighter. The remaining options accurately depict the qualities of various blue dyes and brighteners.