The property used in the industrial preparation of nitrogen and oxygen from air is

The property used in the industrial preparation of nitrogen and oxygen from air is the boiling point. This is because nitrogen and oxygen have different boiling points from the other constituents of air, such as carbon dioxide and water vapor. Nitrogen has a boiling point of -196°C and oxygen has a boiling point of -183°C, while carbon dioxide and water vapor have much higher boiling points. Therefore, the air is cooled and compressed to separate the nitrogen and oxygen from the other gases, based on the differences in their boiling points.