How is the alveoli moist?

There are multiple reasons. First alveoli are coated with a substance known as "surfactant" to prevent them from collapsing. Second, there is a medium for immunoglobulins such as IgA to exist so that...

Yes, all gas-exchange surfaces must be wet for efficient transfer of gases.

The wall is thin to allow rapid andefficient diffusion across of O2 into the blood and CO2 into the alveolar space (the air). It is moist for many reasons but primarily because diffusion in this form...

The Alveoli has a moist lining, Because the gases must be dissolved in water in order to get through the walls..