Concept: This question tests understanding of the ionic basis of an action potential and the restoration of resting membrane potential in neurons.

Why (A) is correct:

I is true: When a neuron receives a stimulus, voltage-gated $N{a}^{+}$ channels open, leading to a rapid influx of $N{a}^{+}$ ions (depolarization). This increased permeability to $N{a}^{+}$ is indeed short-lived because these channels quickly inactivate, and voltage-gated $K^{+}$ channels open, leading to $K^{+}$ efflux (repolarization).

II is false: The resting membrane potential is primarily restored by the efflux of $K^{+}$ ions through voltage-gated $K^{+}$ channels during repolarization, and then maintained by the action of the sodium-potassium pump ($N{a}^{+}-K^{+}$ pump), which actively transports 3 $N{a}^{+}$ ions out and 2 $K^{+}$ ions into the cell. $C{l}^{-}$ ions play a role in maintaining the resting potential but are not directly involved in its restoration after an action potential in the way $N{a}^{+}$ and $K^{+}$ are.

Why other options are wrong:

• B) Both I and II are true: II is false as explained above.
• C) I is false, II is true: I is true and II is false.
• D) Both I and II are false: I is true.

Common Mistake: Students often confuse the roles of different ions and the $N{a}^{+}-K^{+}$ pump during the various phases of an action potential and the restoration of resting potential.

NEET Tip: Remember the sequence: Depolarization ($N{a}^{+}$ influx) \u2192 Repolarization ($K^{+}$ efflux) \u2192 Hyperpolarization (excess $K^{+}$ efflux) \u2192 Restoration ($N{a}^{+}-K^{+}$ pump).

Correct Answer: (A)