Pepsin is an enzyme that plays a crucial role in the digestion of proteins. It is primarily secreted by the stomach. Let's break down the options given and understand why the correct answer is option B.

a) Lungs: The lungs are responsible for respiration and do not secrete pepsin. The main function of the lungs is to oxygenate the blood and remove carbon dioxide.

b) Stomach: The stomach is the correct answer. Pepsin is primarily secreted by the chief cells in the gastric glands of the stomach. These glands are located in the lining of the stomach wall. Pepsinogen, the inactive form of pepsin, is first secreted by the gastric chief cells. When pepsinogen comes into contact with the acidic environment of the stomach, it is activated and converted into pepsin, which then helps in the digestion of proteins.

c) Salivary gland: Salivary glands secrete saliva, which contains enzymes like amylase that help in the digestion of carbohydrates. While saliva does contribute to the overall digestive process, pepsin is not secreted by the salivary glands.

d) Sebaceous gland: Sebaceous glands are present in the skin and are responsible for producing sebum, an oily substance that helps lubricate the skin and hair. Pepsin is not secreted by sebaceous glands.

In conclusion, pepsin is primarily secreted by the stomach, specifically by the chief cells in the gastric glands. Pepsin plays a vital role in breaking down proteins into smaller peptides during digestion.

Pepsin is a stomach enzyme that serves to digest proteins found in ingested food. Gastric chief cells secrete pepsin as an inactive zymogen called pepsinogen. Parietal cells within the stomach lining secrete hydrochloric acid that lowers the pH of the stomach. A low pH (1.5 to 2) activates pepsin thus, option B is right ans