lungs
organ system
Respiratory System
The organ responsible for exchanging oxygen and carbon dioxide during respiration in water is called the gills. Gills are highly specialized structures found in aquatic animals such as fish that facilitate the exchange of these gases between the water and the animal's bloodstream.
The organ is gills.
Lungs.
The respiratory system is responsible for exchanging carbon dioxide from the bloodstream for oxygen to be delivered to tissues. This process occurs in the lungs where oxygen is inhaled and carbon dioxide is exhaled.
lungs
takes in oxygen and releases carbon dioxide.
Respiratory system
I wouldn't exactly characterize it as separating carbon dioxide and oxygen, however, I think the answer you are looking for is the lungs which takes up oxygen into the bloodstream and expels carbon dioxide out of the bloodstream into the lungs so we can breathe it out again.
The lungs are the main organs responsible for breathing. They exchange oxygen from the air with carbon dioxide in the blood, which helps to supply oxygen to the body's cells and remove waste carbon dioxide.
The name of that organ is 'Pair of Lungs'.