Answer:
The correct answer is carbonic acid.
Step-by-step explanation:
The acid-base homeostatic mechanism known as the bicarbonate buffer system involves the balance of bicarbonate ion, carbonic acid, and carbon dioxide in order to sustain pH in the duodenum and in the blood, along with other tissues for maintaining adequate metabolic activities. As with the buffer system, the pH is monitored by the existence of both the weak acid, that is, the carbonic acid, and its conjugate base, like bicarbonate ion, so that any extra base or acid presented to the system getting neutralized. In the bicarbonate buffer system, the carbonic acid reacts with a base to balance the system.