Final answer:
Brunner glands are mucus-secreting glands found in the duodenal submucosa, protecting the intestinal lining by buffering acidic chyme with alkaline mucus. The correct answer is the duodenum.
Step-by-step explanation:
Brunner glands, which are characteristic of a specific region of the small intestine, are located in the duodenum. These are mucus-secreting glands found in the duodenal submucosa. Their primary function is to produce a bicarbonate-rich alkaline mucus that helps to neutralize acidic chyme coming from the stomach. This mucus secretion is crucial for protecting the intestinal lining and providing an optimal pH for digestive enzymes to function. Therefore, the correct answer to the student's question is option 2) duodenum.