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An optical brightening agent works by

  • A.absorbing ultraviolet and emitting blue
  • B.destroying the yellow colouring matter chemically
  • C.coating the fibre with a white pigment layer
  • D.reflecting rather more of the incident light

Answer: A

The fluorescence adds blue light that was not there before, so the fabric returns more visible light than it receives. It removes nothing and is quite different from a bleach. The effect is additive rather than subtractive.

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