Answer:
Both sodium and calcium.
Explanation:
The membrane potential is maintained inside and outside of the cell due to the unequal distribution of the different ions. This membrane potential difference is important for the generation of action potential.
The resting membrane potential is around +30 mV. This is due to the presence of potassium ions. The sodium and calcium ions must enter in the cell to change this membrane potential and generates the action potential in the body.
Thus, the correct answer is option (3).
