Question

how is the air that we inhale purified in our body

Answer 1

the air that we inhale passes through the nose

the nose contains ciliated hair which traps the dust particles and harmful substances like bacteria.

this purifies the inhaled hair.


so
it is better advised to breathe through nose than the mouth

Answer 2

There are tiny, find hair-like outgrowths called cilia inside the nose from where the air passes inside. Larger dust particles get caught in these hair. The air going inside the trachea thus gets filtered. There is also a layer of a sticky substance called muscous. The dust and smoke particles stick to the mucous. Thus the air that we inhale gets purified before it reaches the lungs.