When a neuron’s membrane is at rest, the concentration gradient tends to move potassium the cell and the electrical gradient tends to move it the cell.

outside, inside

Explanation:

When a neuron’s membrane is at rest, the concentration gradient tends to move potassium outside the cell and the electrical gradient tends to move it inside the cell.  When a neuron membrane is at rest, potassium concentration is higher inside the cell and the concentration gradient tends to maintain the system in equilibrium by forcing potassium out of the cell while the electrical gradient works in the opposite direction, trying to move potassium back into the cell.