The correct answer is option 1 - Hydrochloric acid. Gastric juice is the digestive fluid that is produced by the cells lining the stomach and is responsible for breaking down food into smaller particles. Hydrochloric acid is the primary component of gastric juice. It is secreted by the parietal cells in the stomach lining and plays a crucial role in the digestion process. Hydrochloric acid is highly acidic, with a pH level of around 1 to 2, which helps in the breakdown of proteins and also kills harmful microorganisms present in the food. It stimulates the release of enzymes and facilitates the absorption of nutrients in the stomach. It is important for the proper functioning of the digestive system.