Question

Why should we breathe through our nose

Answer 1

Because the nostrils are smaller than the mouth, air exhaled through the nose creates a back flow of air (and oxygen) into the lungs. And because we exhale more slowly through the nose than we do though the mouth, the lungs have more time to extract oxygen from the air we've already taken in.

Answer 2

cz.. it's connected to trachea...which goes to lungs...which further helps in exchange of gases......

that's it