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

Given below are two statements.
Statement $I$: Respiratory membrane is composed of two layers of squamous epithelia,each resting on a thick basement membrane.
Statement $II$: The diffusion of a respiratory gas takes place from lower partial pressure to higher partial pressure of the same.
In the light of above statements,choose the most appropriate answer from the options given below:

What will be the $pO_{2}$ and $pCO_{2}$ in atmospheric air as compared to alveoli?

What is the thickness of the diffusion membrane involved in the exchange of gases in the lungs?

What is correct at the alveoli?

Blood leaving the lungs is rich in: