Answer:
Caustic soda
Step-by-step explanation:
The fractional distillation of air is carried out on liquid air. Before air is liquified, the carbon dioxide content of air is removed using caustic soda. The air is then compressed to a pressure of about 200 atm, sudden expansion of the gas leads to cooling. The process continues until air becomes liquid at -200°C.
Fractional distillation of liquid air usually produces nitrogen and oxygen as major products. nitrogen in obtained first since it has a lower boiling point than oxygen. The gases are then dried, compressed and stored in cylinders.