# How can pure oxygen be obtained from air?

This is not a reaction I would be happy doing, and is the preserve of the specialist. Industrially, they compress, and liquefy air, and then perform a fractional distillation. The normal boiling point of dinitrogen is $- 196$ ""^@C; the normal boiling point of dioxygen is $- 183$ ""^@C, and the difference in principle allows separation. Liquid nitrogen is inert (but it is still a cryogenic liquid that could cause burns); I have written here before, that a Dewar of liquid nitrogen is one of the best fire extinguishers; of course, the fire might light up again after the nitrogen boils off.