The acidic region of gastrointestinal tract is

The correct option is D stomach

• Parietal cells in the stomach secrete roughly two litres of acid a day in the form of hydrochloric acid.
• The acid in the stomach functions to kill bacteria, and to help digestion by solubilizing food.
• The acid is also important to maintain the optimal pH (between 1.8-3.5) for the function of the digestive enzyme pepsin. Hence, the acidic region of the gastrointestinal tract is the stomach.

So, the correct answer is 'stomach'.