​The substance which determines the intensity or brilliance of colour in the dye molecule is​

Correct option is A

The correct answer is (a) Auxochrome. While the chromophore is responsible for producing color in a dye molecule by absorbing specific wavelengths of light, it is the auxochrome that modifies and intensifies the color produced by the chromophore. Auxochromes, such as –OH, –NH₂, –SO₃H, enhance the intensity (brilliance) and depth of the color by altering the light absorption properties of the chromophore.

Information Booster:

• An auxochrome, on the other hand, is a functional group attached to the chromophore that intensifies the color or shifts its wavelength (either bathochromic or hypsochromic shift). Auxochromes enhance the dye’s color brilliance, solubility, and binding ability to fibers.
• Common auxochromes include hydroxyl (–OH), amino (–NH₂), and sulfonic acid (–SO₃H) groups.

Thus, although the chromophore creates the color, it is the auxochrome that determines the intensity and brilliance, which is the specific demand of this question.

Additional Knowledge on Incorrect Options:

• Chromophore (Option b): Responsible for producing the base color but not the intensity or brilliance—that's the role of the auxochrome.
• Auxiliaries (Option c): These are dyeing assistants used during dyeing processes (e.g., leveling agents, dispersing agents) but are not part of the dye molecule’s structure and do not influence color intensity at the molecular level.
• More than one of the above (Option d): Incorrect because only auxochrome directly determines brilliance/intensity of the color.
• None of the above (Option e): Incorrect, since auxochrome is the correct answer.