Final answer:
With the addition of sodium leak channels to a membrane that initially only has potassium leak channels, Na+ ions will enter the cell, causing the RMP to become less negative. However, the RMP will not reach the full Na+ equilibrium potential due to the sodium-potassium pump and more prevalent K+ channels, likely resulting in an RMP closer to -50 mV.
Step-by-step explanation:
The resting membrane potential (RMP) is crucial for the function of neurons and is primarily established by potassium (K+) and sodium (Na+) ions. Initially, the presence of only potassium leak channels creates a negative RMP of approximately -90 mV as potassium ions tend to leave the cell. When sodium leak channels are added to the membrane, there is a tendency for Na+ to move inside due to its concentration gradient and because of the relative permeability of the membrane to Na+ and K+ ions.
As Na+ enters the cell, it brings positive charges, thus making the interior less negative and leading to a change in the RMP towards the Na+ equilibrium potential. However, due to the action of the sodium-potassium pump (which moves 2 K+ inside and 3 Na+ outside per ATP consumed) and the presence of more K+ leak channels than Na+ channels, the RMP will not reach the full equilibrium potential of Na+ (+60 to +70 mV), but will instead stabilize closer to the K+ equilibrium potential. The most likely RMP value with Na+ leak channels added would typically be higher than -90 mV but less positive than +60 mV, so the correct answer to the question is (b) -50 mV.