The correct answer would be a.Resting membrane potential (RMP).
Resting membrane potential (RMP) refers to the potential difference found across the cell membrane of cell at rest.
It is created due to the unequal distribution of ions (such as Na⁺, K⁺, Cl⁻, Ca⁺⁺ etc) across the plasma membrane. It depends on the concentration gradient of ions across the plasma membrane as well as on its permeability for each type of ion.
The value of RMP may vary with the type of cell for example, RMP for neuron is around -70 mV, for skeletal muscle it is around - 90 mV etc. Negative value suggests that there is an excess of negative charge inside the cell as compared to the outside of the cell.
Resting Membrane Potential
The resting membrane potential refers to the difference in voltage between the inside and outside of the cell membrane when the cell is at physiological rest. It should be noted that the cell membrane is a selective semipermeable barrier, which only allows the transit through it of certain molecules and prevents the transit of others.
This selectivity causes an uneven distribution of charged particles (ions), as the membrane only accepts some types of ions.
Now, in the case of neurons, which are electrically excitable nerve cells; the transport of electrical signals is due to these changes in the permeability and asymmetric distribution of ions (mainly sodium and potassium) when the neuron is not excited (at rest).