To solve this problem, we need to identify the cells whose secretion protects the lining of the gastrointestinal tract from various enzymes. Let's analyze each option:$\newline \bullet$Chief Cells:$\newline$ - Chief cells are found in the stomach and are responsible for secreting pepsinogen, a precursor to the enzyme pepsin, which aids in protein digestion.$\newline$ - They do not secrete substances that protect the gastrointestinal lining.$\newline \bullet$Goblet Cells:$\newline$ - Goblet cells are specialized epithelial cells found throughout the gastrointestinal tract.$\newline$ - They secrete mucus, which forms a protective barrier on the lining of the gastrointestinal tract.$\newline$ - This mucus protects the lining from digestive enzymes and acidic conditions.$\newline$ - Therefore, goblet cells are responsible for protecting the gastrointestinal lining.$\newline \bullet$Oxyntic Cells:$\newline$ - Oxyntic cells, also known as parietal cells, are found in the stomach lining.$\newline$ - They secrete hydrochloric acid (HCl) and intrinsic factor, which are important for digestion and vitamin B12 absorption, respectively.$\newline$ - They do not provide protective secretions for the gastrointestinal lining.$\newline \bullet$Duodenal Cells:$\newline$ - Duodenal cells, specifically Brunner's glands, secrete an alkaline mucus that helps neutralize stomach acid in the duodenum.$\newline$ - While they contribute to protection in the duodenum, they are not responsible for the overall protection of the gastrointestinal tract lining.$\newline$Based on the analysis, the correct option is Option 2: Goblet Cells, as they secrete mucus that protects the lining of the gastrointestinal tract.