Why is liquid oxygen coloured?

Answer 1

The blue color of oxygen results from the interaction of light with transient complexes of two oxygen molecules. This complex of four oxygen atoms can absorb visible photons of various colors (determined by the vibrational states of the complex).

This process actually does occur in gaseous oxygen, as well. However, the intensity of the color is proportional to the density of two-oxygen-molecule complexes, and therefore to the oxygen molecule density squared. Since the density of liquid oxygen is about 1000x higher than gaseous oxygen, the liquid is about a million times as blue as the gas.

Answer 2

liquid oxygen is blue because of it's strong Paramegnetism Effect.

Paramagnetism is a form of magnetism that occurs only in the presence of an externally applied magnetic field. Paramagnetic materials have a relative magnetic permeability greater or equal to unity, i.e. a positive magnetic susceptibility, and hence are attracted to magnetic fields.

Answer 3

Liquid oxygen has a pale blue color due to its unique molecular structure. When light interacts with the oxygen molecules, it absorbs certain wavelengths in the red part of the spectrum, giving it a bluish tint.

Answer 4

liquid Oxygen is blue in color.
The liquid oxygen is blue incolour because of unpaired electron in it.