Question

Auxochromes of dyes are generally called as ___________.
A ) colour intensifiers
B ) colour depressors
C ) A and B
D ) None of the above

Answer 1

Hint: Auxochromes makes the dye colored. Auxochromes help to achieve colour or they increase the intensity of the colour.

Complete answer:
Aromatic compounds containing auxochromes are dyes. They include benzene nucleus and have extensive delocalization of pi electrons. The extent of delocalization is different for different structures. So lights of different wavelengths and energies can be absorbed. The energy of the light absorbed depends on the energy of the electronic transitions. These electronic transitions occur because the electrons of chromophore are excited from ground state to excited state. When chromophore absorbs light in the visible region, the electrons are excited. Chromophores affect the delocalization of pi electrons. Hence, dye can absorb lights of different wavelengths.
When auxochrome and chromophore are meta to each other, the colour is not affected. But if auxochrome and chromophore are either ortho or para to each other, the colour is intensified as the extent of delocalization increases.
Auxochrome makes the dye colored.

Hence, the correct option is the option A.

Note: Auxochrome alters the light absorbing ability of chromophore. Auxochrome, on its own, cannot make the dye coloured. But auxochrome can increase the intensity of the colour. Auxochrome has atoms having one or more lone pairs of electrons. These lone pairs of electrons can come in conjugation with the pi electron system of chromophore.