Question

Which structure of lungs is directly involved in $O_2/C{O}_2$ exchange between air and blood capillaries $?$

Answer 1

Alveoli

Each primary bronchi undergoes repeated divisions to give out secondary and tertiary bronchi and then very thin bronchioles.

Each terminal bronchiole gives rise to very thin, irregularly shaped, vascularized air sacs called alveoli. They are the sites of gaseous exchange. The exchange of $O_2$ and $C{O}_2$ occurs in between alveoli and blood capillaries.

Final answer:

$\left(C\right)$ Alveoli