Which of the following groups is not an auxochrome ?
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A dye molecule is made up of two different parts (i) Chromophore (Greek : chroma-colour, phoros -bearing) and (ii) Auxochromes (Greek : aux。= increase, chroma colour). The groups which produce colour in a compound, i.e. chromophores are usual unsaturated groups like nitro,nitroso, azo, azoxy, carbonyl and olefinic bonds. Auxochromes are usually acidic /basic functional groups like -OH, -COOH, -SO3H, -NH2, -NHR, -NR2.
A compound containing only a chromophore may be a coloured material but not a dye, e.g., azobenzene is red coloured but not a dye whereas p-aminoazobenzene (aniline yellow) is a dye.