The sodium-potassium pump is an essential membrane protein found in all human cells, including neurons. It plays a crucial role in maintaining the resting membrane potential and regulating the concentration of sodium (Na+) and potassium (K+) ions inside and outside the neuron. The correct answer to the question is option 'D', which states that the sodium-potassium pump transports K+ into the neuron and Na+ out of the neuron.

Explanation:

1. Resting Membrane Potential:
- The resting membrane potential of a neuron is the electrical potential difference across its cell membrane when it is not conducting any electrical impulses.
- It is maintained by the sodium-potassium pump, among other ion channels and transporters.
- The resting membrane potential is typically around -70 millivolts (mV) in neurons.

2. Sodium-Potassium Pump:
- The sodium-potassium pump is an active transport protein that uses energy from ATP hydrolysis to transport Na+ and K+ ions across the cell membrane.
- It is also known as the Na+/K+-ATPase pump.

3. Transport Mechanism:
- The sodium-potassium pump transports three Na+ ions out of the neuron for every two K+ ions pumped into the neuron.
- This creates an electrochemical gradient, as there is a higher concentration of Na+ ions outside the neuron and a higher concentration of K+ ions inside the neuron.
- The pump maintains these concentration gradients to ensure proper neuronal function.

4. Sodium (Na+) Transport:
- The pump actively transports Na+ ions out of the neuron against their concentration gradient.
- This helps to maintain a lower concentration of Na+ ions inside the neuron and a higher concentration outside the neuron.
- This outward movement of Na+ ions contributes to the negative resting membrane potential.

5. Potassium (K+) Transport:
- The pump actively transports K+ ions into the neuron against their concentration gradient.
- This helps to maintain a higher concentration of K+ ions inside the neuron and a lower concentration outside the neuron.
- This inward movement of K+ ions also contributes to the negative resting membrane potential.

6. ATP Hydrolysis:
- The sodium-potassium pump requires ATP hydrolysis to drive its active transport process.
- ATP is converted to ADP and inorganic phosphate (Pi) during this process, releasing energy that is used to change the conformation of the pump and transport the ions.

In conclusion, the sodium-potassium pump transports Na+ ions out of the neuron and K+ ions into the neuron. This transport is essential for maintaining the resting membrane potential and the concentration gradients of these ions, which are crucial for proper neuronal function.