Final answer:
Sodium (Na+) will move more frequently through a small cation channel at a resting membrane potential of -70 mV due to its higher concentration outside the cell and the existing concentration gradient. The correct option C.
Step-by-step explanation:
Considering a resting membrane potential of -70 mV, the cation that will move more frequently through a small cation channel is sodium (Na+). This is due to the high concentration of Na+ outside the cell and lower concentration inside, creating a strong concentration gradient.
Moreover, the inside of the cell is negatively charged compared to the outside due to the action of the sodium-potassium pump, which actively transports three sodium ions out for every two potassium ions it brings in.
Potassium (K+), although more concentrated inside, has channels that are open less frequently, making the inward movement of Na+ dominant.
Hence, Option C is correct.