Question

Choose the odd one out in each of the following groups of four items each:

(d) Trachea, ciliated epithelium, mucus, diffusion.

Answer 1

The correct answer is diffusion.

Trachea is lined by ciliated epithelium which secretes mucus by specialised cells.
Diffusion is a process by which gases exchange which occur in lung alveoli but not in trachea.

So, the odd one is diffusion.