Final answer:
The nasal cannula is the medical device used most often for the delivery of oxygen therapy.
Step-by-step explanation:
The medical device used most often for the delivery of oxygen therapy is the nasal cannula. A nasal cannula is a small plastic tube that is placed in the nostrils and delivers oxygen directly to the patient's lungs. It is a comfortable and convenient option for oxygen delivery, allowing the patient to eat, drink, and talk while receiving oxygen.