Partial pressure for oxygen and $CO_2$ is represented as

Amount of $CO_{2}$ in expired air is about (in $\%$)

Mammalian lungs have an enormous number of minute alveoli (air sacs). This is to allow:

The given figure shows a small part of the human lung where gas exchange occurs. Identify the part $A, B, C,$ or $D$ correctly with its function from the given options.

What is the partial pressure of $CO_2$ in the alveolar air?

The partial pressures (in $mm \ Hg$) of oxygen $(O_{2})$ and carbon dioxide $(CO_{2})$ at the alveoli (the site of diffusion) are: