The correct answer is option 2: Pepsin. Pepsin is an enzyme produced in the stomach that is responsible for breaking down proteins. It is produced and released in its inactive form, pepsinogen, by cells in the stomach lining. When pepsinogen comes into contact with the acidic environment of the stomach, it is converted into pepsin. Pepsin then begins the process of hydrolysis, which breaks down the peptide bonds in proteins, turning them into smaller peptides. This process is essential for the digestion and absorption of proteins in the body. It is important to note that while trypsin is another enzyme that digests proteins, it is produced in the pancreas and acts on proteins in the small intestine, not in the stomach.