Final answer:
The process of molecules moving from an area with a higher concentration to a lower concentration is called diffusion, which is a type of passive transport that doesn't require energy and occurs until equilibrium is reached.
Step-by-step explanation:
The process in which molecules, ions, or particles move from an area of higher concentration to a lower concentration is known as diffusion. During this natural process, substances will continue to move until an equilibrium is reached, meaning the concentration of molecules will become equal on both sides of a membrane. This is a form of passive transport, which doesn't require energy since molecules are moving down the concentration gradient. It is crucial for various physiological processes, including the exchange of oxygen and carbon dioxide in the body.
Although osmosis is similar to diffusion, it specifically refers to the movement of water across a semi-permeable membrane, from an area of low solute concentration to an area of high solute concentration, hence option a) Osmosis is not the correct answer for the question presented.