Concept: This question tests your understanding of how the resting membrane potential is established and maintained in a neuron, focusing on the active transport mechanisms involved.

Why (A) is correct: The Na⁺-K⁺ pump (sodium-potassium pump) is an active transport mechanism that continuously pumps three Na⁺ ions out of the neuron for every two K⁺ ions it pumps into the neuron. This differential pumping, along with the differential permeability of the membrane to Na⁺ and K⁺ ions (more permeable to K⁺), creates and maintains the resting membrane potential, which is an electrical charge difference across the neuronal membrane.

Why other options are wrong:

• (B) Action potential: An action potential is a transient reversal of the membrane potential, not what maintains the general charge.
• (C) Resting potential: The resting potential is the electrical charge itself, not the mechanism that maintains it.
• (D) Voltage-gated channels: These channels open and close in response to changes in membrane potential and are crucial for generating action potentials, but they do not primarily maintain the resting charge.

Common Mistake: Students often confuse the resting potential (the state) with the Na⁺-K⁺ pump (the mechanism that maintains it).

NEET Tip / Mnemonic: Remember "3 Na Out, 2 K In" for the Na⁺-K⁺ pump's action, which is crucial for maintaining the negative resting potential inside the neuron.

Correct Answer: (A)