Which of the following factors affect the rate of diffusion?

What is the direction of the concentration gradient for $CO_2$ and $O_2$ during gas exchange?
$CO_2$ gradient $\quad$ $O_2$ gradient

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 is the main site of the human respiratory system where the exchange of gases occurs?

Which of the following statements is $NOT$ correct?

Under normal physiological conditions,$100 \, mL$ of oxygenated blood delivers how much $CO_2$ to the alveoli?