When the membrane is at the potassium equilibrium potential, in which direction (in or out) is there a net movement of potassium ions? 

When the membrane is at the potassium equilibrium potential (Eₖ), there is no net movement of potassium ions (K⁺) across the membrane. This state occurs when the electrical force pulling K⁺ ions back into the cell exactly balances the diffusional force driving them out. Thus, at this equilibrium potential, the movement of K⁺ ions into and out of the cell is equal, resulting in no net movement.