IBDP Chemistry Question Analysis Topic: Chemistry -
Explain why: Halogens are coloured and the colour deepens on moving down in the group from fluorine to iodine.
Because of their low ionization energy, halogens are colored, which causes the electron to become excited when absorbing visible light. Thus, the molecule receives the complementary color from the reflected light.
Moving down the group, the color deepens as the atomic radii of the elements grow from fluorine to iodine. As a result, low energy light (higher wavelength i.e. toward red) is absorbed.
End of analysis. Great!