It is a rhythmic contraction and relaxation in the wall of food pipe through which food is pushed down in the Oesophagus.

Peristalsis in Oesophagus:

Peristalsis is the rhythmic contraction and relaxation of muscles responsible for the movement of food through the digestive system. In the case of the oesophagus, peristalsis is the primary mechanism responsible for pushing food from the mouth to the stomach.

Function of Oesophagus:
The oesophagus is a muscular tube that connects the mouth to the stomach. Its primary function is to transport food and liquids from the mouth to the stomach so that the digestive process can continue.

Process of Peristalsis in Oesophagus:
When food is swallowed, it enters the oesophagus, which begins a series of coordinated muscle contractions known as peristalsis. The contractions begin at the top of the oesophagus and move downward to the stomach. As the muscles contract, they push the food toward the stomach in a wave-like motion.

Role of Saliva:
While saliva does help to lubricate food and make it easier to swallow, it is not the primary mechanism responsible for moving food through the oesophagus. Saliva only plays a minor role in the digestive process.

Other Mechanisms:
Diffusion and turgor pressure are also not responsible for the movement of food through the oesophagus. Diffusion is the process by which molecules move from an area of high concentration to an area of low concentration, and turgor pressure is the pressure exerted by water inside of plant cells.

Conclusion:
Therefore, the correct answer is option B, peristalsis, which is the primary mechanism responsible for pushing food through the oesophagus.