What is the role of a mordant, such as alum, in dyeing?
Correct answer A. It binds the dye to the fibre by forming an insoluble complex
Explanation
Mordant dyes cannot bind to fibres on their own. A metal salt, such as an aluminium or chromium salt, forms a coordination complex (a lake) linking the dye to the fibre, improving fastness. Alizarin is a classic example.
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