The majority of water molecules moving across plasma membranes by osmosis do so via a process that is most similar to

The answer is Facilitated Diffusion

Explanation:

Osmosis is most similar to facilitated diffusion.

Osmosis can be defined as : Osmosis is the movement of water molecules across a semi-permeable membrane, down a concentration gradient from a low concentrated solution into a more concentrated solution.

Facilitated diffusion is defined as: Facilitated diffusion is the flow of molecules requiring the aid of a protein, across a membrane, down a concentration gradient  from a low concentrated solution into a more concentrated one.

the product of the pressure and volume is also constant