Which statement correctly describes the effect of UV light on the reaction mixture?

Which statement correctly describes the effect of UV light on the reaction mixture?

• A. Orange-yellow colour goes to colourless.
• B. The colour changes from brown to purple.
• C. The mixture remains unchanged.
• D. A solid forms.

Answer: (A)

Photochemical effects of UV light on colored organic compounds. UV photons provide enough energy to break bonds or rearrange structures, especially in molecules with conjugated pi-systems that give color by absorbing visible light. If the chromophore is disrupted or degraded, the visible absorption diminishes and the solution becomes colorless. This decolorization under UV is a common sign that a photolytic reaction is breaking the color-producing part of the molecule. The option describing the orange-yellow colour fading to colourless matches this idea of decolorization due to photochemical change. A change to purple would require forming a new strongly colored species, which is less typical under simple photolysis; remaining unchanged would imply UV has no effect, which contradicts the observed color loss; and forming a solid would be precipitation rather than a color change driven by light.

Photochemical effects of UV light on colored organic compounds. UV photons provide enough energy to break bonds or rearrange structures, especially in molecules with conjugated pi-systems that give color by absorbing visible light. If the chromophore is disrupted or degraded, the visible absorption diminishes and the solution becomes colorless. This decolorization under UV is a common sign that a photolytic reaction is breaking the color-producing part of the molecule.

The option describing the orange-yellow colour fading to colourless matches this idea of decolorization due to photochemical change. A change to purple would require forming a new strongly colored species, which is less typical under simple photolysis; remaining unchanged would imply UV has no effect, which contradicts the observed color loss; and forming a solid would be precipitation rather than a color change driven by light.