What is correct at the alveoli?

Which of the following factors affect the rate of diffusion?

The exchange of gases in the alveoli of the lungs takes place by

Which surface of a plant leaf is better adapted for gas exchange?

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: