The process of molecules moving across a membrane from high to low concentration using specific membrane proteins, but without energy, is called

The correct answer is- facilitated diffusion

Explanation:

In facilitated diffusion molecules(solutes) are moved from area having a high concentration of solute towards the area having low solute concentration through a semipermeable membrane with the help of specific proteins is called facilitated diffusion.  

As molecules move along the concentration gradients so no energy consumption is required in facilitated diffusion. Transport proteins like channel proteins are used to transport the molecules across the cell.  

The rate of transport is higher in facilitated diffusion than simple diffusion. Polar and charged molecules can be diffused by facilitated diffusion.