In humans,where does the exchange of gases take place?

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:

Which of the following factors affects the diffusion of gases?

Which of the following factors is most necessary for an efficient respiratory surface?

What is the partial pressure of Oxygen $(PO_2)$ and Carbon dioxide $(PCO_2)$ in the alveoli?

Which of the following is true for the exchange part of the respiratory system?