Liquid oxygen is pale blue and can be attracted by magnets.

Oxygen becomes a liquid at its boiling point of -183°C (-297°F) under standard atmospheric pressure. This liquid state reveals a distinct pale blue color caused by the absorption of red light as oxygen molecules collide and absorb photons. This specific electronic transition is known as a 'forbidden transition' which becomes possible in the dense liquid phase.The magnetic nature of oxygen is explained by Molecular Orbital Theory. Unlike most substances where electrons exist in pairs, a dioxygen molecule (O2) has two unpaired electrons in its outermost antibonding orbitals. These unpaired electrons possess a magnetic dipole moment, making the entire molecule paramagnetic. This discovery is often credited to Robert S. Mulliken, who won the Nobel Prize in Chemistry in 1966 for his work on molecular orbital theory.In a laboratory setting, this effect is demonstrated using neodymium magnets or powerful electromagnets. When liquid oxygen is poured through a magnetic field, the magnetic force overcomes gravity, causing the liquid to stick to the poles. This property is unique among common liquids, as liquid nitrogen, which looks similar, is diamagnetic and is actually repelled by magnets.This magnetic property has practical applications in aerospace engineering and physics research. Engineers must account for these magnetic forces when designing fuel systems for rockets that use liquid oxygen (LOX) as an oxidizer. Understanding these molecular structures helps scientists predict how oxygen will behave under extreme pressures and temperatures in space.