Paramagnetism of Oxygen
Substances that contain unpaired electrons exhibit a behavior called paramagnetism. Paramagnetic substances are attracted to a magnet. For example, Iron metal is paramagnetic, and it can be picked up with a magnet. On the other hand, blackboard chalk is not paramagnetic, so it cannot be picked it up with a magnet. When we pour liquid nitrogen through the poles of a magnet, it will just passes through. Nitrogen is not paramagnetic, thus it doesn't have any unpaired electrons. On the other hand, if we pour liquid O2 through the poles of the magnet, an O2 bridge forms because liquid O2 is paramagnetic.
What this video demonstrating the paramagnetism of liquid oxygen.