Concept: This question tests your understanding of the resting membrane potential in neurons, specifically the differential permeability of the axonal membrane to ions.

Why (D) is correct: When a neuron is at rest (not conducting an impulse), its axonal membrane is comparatively more permeable to K⁺ ions and nearly impermeable to Na⁺ ions. This differential permeability, along with the action of the Na⁺/K⁺ pump, is crucial for maintaining the resting membrane potential, which is typically around -70mV. The higher permeability to K⁺ allows K⁺ ions to leak out of the cell down their concentration gradient, contributing to the negative charge inside.

Why other options are wrong:

• (A) This describes the state during depolarization (action potential generation), not the resting state.
• (B) If permeability were equal, the resting potential would not be established or maintained effectively.
• (C) The membrane is permeable to some extent to K⁺ ions even at rest, which is essential for the resting potential.

Common Mistake: Students often confuse the permeability of the membrane during the resting state with its permeability during an action potential.

NEET Tip / Mnemonic: Remember that at Rest, the membrane is more permeable to K⁺ (potassium) because 'R' and 'K' are close in the alphabet, and K⁺ 'leaks' out, making the inside negative.

Correct Answer: (D)