The basic answer is it helps to begin the breakdown of food and start the digestive process (which actually starts with the saliva in your mouth when you take a bite of food)
it helps to begin the breakdown of food and start the digestive process.
To chemically break down the food you eat in the digestive process.
Yes it is. The proper name for it is Gastric Acid.
Not in any real quantity, if any. Though acid reflux can cause hydrochloric acid from the stomach to be pushed up to the esophagus.