Both NO and `NO_(2)` have odd number of electrons. NO is colourless, but `NO_(2)` is coloured. Why?

Explanation

`NO_(2)` molecule, colour is explained based on the presence of unpaired electron, which can be excited easily by the absorption of visible light. In NO molecule, the odd electron is also involved in bonding between two bonded atoms, the excitation of which can be possible only in ultraviolet region. Thus NO is colourless.