**Core Concept:** Repolarization of nerve action potential is the process by which the membrane potential of a neuron returns to its resting state after depolarization, preventing continuous neuronal firing and allowing for proper neuronal function. This is crucial for the transmission of nerve impulses and maintaining homeostasis within the nervous system.

**Why the Correct Answer is Right:** Repolarization of a nerve action potential is primarily due to the inactivation of voltage-gated sodium (Na+) channels, which leads to a decrease in the influx of sodium ions and a subsequent reduction in membrane depolarization. As a result, the membrane potential returns to its resting state, allowing the neuron to rest and prepare for another action potential. This process is essential for the proper functioning of neurons and maintaining homeostasis within the nervous system.

**Why Each Wrong Option is Incorrect:**

A. **Option A:** The statement "A. Depolarization is due to the closure of potassium channels" is incorrect because depolarization is caused by the opening of voltage-gated sodium channels, not the closure of potassium channels. Potassium channels play a crucial role in repolarization, but they are not responsible for depolarization.

B. **Option B:** The statement "B. Depolarization is due to the opening of calcium channels" is incorrect because calcium channels are primarily involved in neurotransmitter release and muscle contraction, not generating action potentials. Sodium channels are responsible for depolarization.

C. **Option C:** The statement "C. Repolarization is due to the closure of calcium channels" is incorrect because calcium channels are primarily involved in neurotransmitter release and muscle contraction, not repolarization. Potassium channels play a crucial role in repolarization, specifically the rapid rectifier potassium (Kv7) channels.

D. **Option D:** The statement "D. Depolarization is due to the closure of potassium channels" is incorrect because potassium channels are primarily involved in repolarization, specifically the delayed rectifier potassium (Kv1) channels. These channels open during repolarization, causing potassium ions to flow out of the neuron, thus returning the membrane potential towards its resting state.

**Clinical Pearl:** Understanding the correct mechanisms of depolarization and repolarization is essential for understanding neuronal function and the proper transmission of nerve impulses within the nervous system. These processes are crucial for maintaining homeostasis in the body and ensuring efficient communication between cells.