ion

The OH

ion, also known as the hydroxide ion, is colorless. This is due to the fact that the OH- ion is a simple anion with a single oxygen atom bonded to a single hydrogen atom. The lack of complex electronic transitions or d-d transitions in the electron configuration of the oxygen atom results in no significant absorption or emission of light in the visible spectrum, thus rendering the ion colorless.

The colorless nature of the OH- ion can be further supported by experimental data. For instance, studies have shown that the absorption spectrum of the OH- ion in the gas phase is primarily in the ultraviolet region, with no significant absorption in the visible range. This is consistent with the electronic configuration of oxygen, which has a 2p^4 configuration, leading to transitions that occur at higher energy levels. Additionally, the colorless nature of the OH- ion in solution is also well-documented, as it is commonly used in various chemical reactions and does not impart any color to the solutions it is present in.