Which of the following is present in our stomach? 

Hydrochloric acid 

The correct answer is option 1. Hydrochloric acid.

Hydrochloric acid (HCl) is a strong acid present in the gastric juices of the stomach. It plays a crucial role in the digestive process by aiding in the breakdown of food and the digestion of nutrients.

Here is how hydrochloric acid functions in the stomach:

1. Activation of Enzymes: HCl activates the enzyme pepsinogen, converting it into pepsin. Pepsin is essential for the digestion of proteins in the stomach.

2. Acidic Environment:  The stomach maintains an acidic environment (low pH) due to the presence of hydrochloric acid. This acidic environment is necessary for the optimal activity of digestive enzymes and helps break down complex food molecules.

3. Killing Bacteria:  Hydrochloric acid also serves as a defense mechanism by helping to destroy or inhibit the growth of harmful bacteria or microorganisms that may be present in ingested food.

The stomach's acidic environment is essential for the initial stages of digestion, particularly the breakdown of proteins into smaller peptides. It is important to note that the lining of the stomach is adapted to withstand the corrosive effects of hydrochloric acid.

Disruptions in the production of hydrochloric acid can lead to digestive issues, and conditions such as gastritis or gastric ulcers may be associated with imbalances in stomach acid levels.