Answer:
Option). the mucus coating secreted by the epithelial cells of the stomach
Explanation:
Stomach produces gastric juices, which is very acidic in nature, due to hydrochloric acid.
In normal conditions, surface epithelial cells of stomach are present in stomach inner wall, which are mucus-producing cells. These cells secret mucus and protect the inner side of stomach from concentrated gastric acid.
Stomach ulcers are sores in stomach wall, due to break in its inner lining by gastric acid, due to inhibition of mucus secretion due to various factors.
Thus, the correct answer is second option.