What is the approximate pH value in the mouth, duodenum, ileum and small intestine?

• A. pH 2
• B. pH 7-9
• C. pH 12
• D. pH 5

Answer: (B)

In these parts of the digestive tract, the environment is kept close to neutral or mildly alkaline to support enzyme activity and protect the intestinal lining. The mouth has saliva that maintains roughly neutral conditions, and as chyme moves into the duodenum and ileum, bicarbonate from the pancreas neutralizes stomach acid, pushing the pH toward about 7 to 9. This alkaline shift is important because many digestive enzymes in the small intestine work best around neutral to slightly basic pH. Among the given options, 7-9 best matches this range across the mouth and the small intestine, whereas 2 is too acidic for these regions, 12 is far too alkaline, and 5 is also not representative of the small intestine.