The correct answer is - Hydrochloric acid from the stomach is escaping through the cardiac sphincter into the esophagus.
The burning feeling often begins in the chest shortly after eating food. This is also called heartburn. It occurs when hydrochloric acid (HCl) from stomach comes into the esophagus. The cardiac sphincter (a band of muscle at the bottom of esophagus) is normally closes when there is no eating. It prevents back flow of food and acid into esophagus. If it closes prematurely, hydrochloric acid can come back into the esophagus causes heartburn.