Which would have a greater impact on the resting potential lowering the extracellular Na concentration by 2 mM or lowering extracellular K concentration by 2 mM?

Lowering the extracellular K+ concentration by 2 mM would have a greater impact on the resting potential than lowering the extracellular Na+ concentration by the same amount. This is because the resting potential is primarily determined by the permeability of the membrane to K+, and a decrease in K+ concentration outside the cell would increase the gradient and drive the resting potential more positive. In contrast, changes in Na+ concentration have a lesser effect on resting potential since the membrane is less permeable to Na+ at rest.