The main cause of acidity in the stomach is

release of extra gastric acids which decrease the pH level

The main cause of acidity in the stomach is 1. release of extra gastric acids which decrease the pH level.

Gastric acid is a digestive fluid that is produced by the stomach. It helps to break down food and kill bacteria. However, if too much gastric acid is produced, it can lead to acidity in the stomach. This is because gastric acid is acidic, with a pH of around 2. When the pH of the stomach drops below 4, it can cause discomfort and pain.

Indigestion and pain in the large intestine are not the main causes of acidity in the stomach. Indigestion is a disorder of the digestive system that can cause symptoms such as heartburn, nausea, and vomiting. Pain in the large intestine can be caused by a variety of factors, including constipation, diarrhea, and inflammatory bowel disease. However, neither indigestion nor pain in the large intestine directly causes acidity in the stomach.

The increase in pH level in the stomach and the release of extra bile juice which increases alkaline medium in the stomach are both opposite of acidity. Therefore, they cannot be the main causes of acidity in the stomach.