Human stomach produces acid ‘X’ which helps in digestion of food. Acid ‘X’ is :

The human stomach contains gastric glands in its walls that secrete gastric juice, which primarily consists of hydrochloric acid (HCl), the protein-digesting enzyme pepsin, and mucus [c1]. Hydrochloric acid creates an acidic medium (low pH) necessary for pepsin to become active and break down proteins into simpler components [c1][c3]. Additionally, this acid serves a protective role by killing harmful bacteria that may enter the body through food [c3][t8]. While the acid is highly corrosive, the stomach lining is protected from damage by a layer of mucus [c1][c3]. During indigestion, an excess of hydrochloric acid can cause pain and irritation, which is typically neutralized using antacids like magnesium hydroxide [c2][t4]. Other options like acetic acid (vinegar), methanoic acid (formic acid), and citric acid are organic acids found in plants or insects rather than being the primary digestive acid of the human stomach [t3][t6].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.3 > p. 85
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 2: Acids, Bases and Salts > pH in our digestive system > p. 27
3. [3] Science-Class VII . NCERT(Revised ed 2025) > Chapter 9: Life Processes in Animals > Stomach > p. 125