What is the name of the process in which molecules move from an area of high concentration to an area of low concentration across a selectively permeable membrane?

Diffusion.

Explanation:

when molecules move from an area of high concentration (large amount) to an area of low concentration (low amount). ... In simple diffusion, molecules that are small and uncharged can freely diffuse across a cell membrane.

not too sure but maybe in the hot springs.

all matter is made up of atoms

in any element all atoms are the same

elements in a compound are always in a constant ratio: apex