What part of the respiratory system connects the oesophagus and trachea and is the passage for both food and air?

Hint: The oesophagus is a muscular tube-like organ that develops from the endoderm primitive gut and is placed between the lower border of the laryngeal section of the pharynx and the cardia of the stomach. It is 25–28 cm long and around 2 cm in diameter.

Complete answer:
The pharynx is the area of the throat behind the mouth and nasal cavity, as well as the area above the oesophagus and trachea, which are the tubes that lead to the stomach and lungs. It can be found in both vertebrates and invertebrates, albeit the structure differs depending on the species. The pharynx transports food and air from the stomach to the oesophagus and larynx. The epiglottis is a cartilage flap that prevents food from entering the larynx.
The pharynx is formed by two sets of pharyngeal muscles, which govern the shape of the lumen. They are divided into two layers: a longitudinal inner layer and a circular outer layer.
The pharynx is responsible for transporting food from the mouth to the oesophagus. It also transports air to the larynx from the nasal and oral canals. It is also utilised in human speech to articulate pharyngeal sounds. When swallowing, the epiglottis restricts the larynx, directing food to the oesophagus. When there is no food, however, the epiglottis opens to allow air into the larynx.

Note:
The pharynx is found in all vertebrates and is used for both feeding and breathing. The pharynx emerges from a sequence of six or more outpocketings on the lateral sides of the head in all vertebrates throughout development. Pharyngeal arches are outpocketings that give rise to a variety of structures in the skeletal, muscular, and circulatory systems. The pharynx has different structures in different animals.