Concept: This question tests your understanding of the resting membrane potential in neurons and the crucial role of the sodium-potassium pump in maintaining it.

Why (B) is correct:

The sodium-potassium pump actively transports three Na⁺ ions out of the neuron for every two K⁺ ions it transports into the neuron. This action is vital for:

• II. The resting potential of $-70\mathrm{mV}$: The pump maintains the concentration gradients of Na⁺ and K⁺ across the neuronal membrane, which is fundamental for establishing and maintaining the resting membrane potential (typically around $-70\mathrm{mV}$). If the pump stops, these gradients will dissipate, and the resting potential will be lost.
• III. Movement of sodium and potassium ions along the axolemma: The pump is directly responsible for the active transport (movement against concentration gradient) of Na⁺ and K⁺ ions across the axolemma. If it stops, this specific movement ceases.

Why other options are wrong:

• I. Movement of negatively charged protein along the axolemma: Proteins are large molecules and generally do not move across the axolemma; they are synthesized inside the neuron.
• IV. Concentration of Nissl's granule: Nissl's granules are aggregates of rough endoplasmic reticulum and ribosomes involved in protein synthesis. Their concentration is not directly affected by the immediate cessation of the sodium-potassium pump.

Common Mistake: Students sometimes confuse the role of ion channels (passive movement) with the sodium-potassium pump (active movement) in maintaining the resting potential.

NEET Tip: Remember that the sodium-potassium pump is an active transport mechanism, meaning it requires ATP to function and moves ions against their concentration gradients to maintain the resting potential.

Correct Answer: (B)