The blood is oxygenated in which of the following organs?

The lungs are the primary organs of the respiratory system, and their main function is to exchange respiratory gases (oxygen and carbon dioxide), with the bloodstream. 

The bronchioles are small airways that branch off from the trachea (windpipe) and lead to the alveoli, which are small thin-walled sacs. These are the site of gaseous exchange in the lungs. They are surrounded by capillaries, which allow for the exchange of respiratory gases by diffusion. Oxygen from the air in the alveoli diffuses into the bloodstream, while carbon dioxide from the bloodstream diffuses into the alveoli to be exhaled out of the body. 

This process of gas exchange is vital for the body to obtain the oxygen it needs for cellular respiration, which is the process that produces energy for the body's cells.