Why is nose breathing preferable to mouth breathing

Because the nose is well adapted to breathing than the mouth. The nose warms the air before it reached the lungs. It also filters out the dust and foreign particles using the nose hairs and mucus. The mucus also has antibacterial properties hence mitigating bacterial infections.

Nasal breathing is preferred over mouth breathing because most of the oxygen is absorbed from the air while exhaling. The outlet of nose is smaller than the mouth due to which nose creates more air pressure which leads to slower exhalation and greater time for oxygen to get absorbed.

Nose is connected to lungs and heart through nerves and not breathing through nose will lead to disturbed heart rate and blood pressure.