Concept: This question tests your understanding of the ionic gradients across a neuron's membrane during its resting state and the direction of ion movement driven by concentration differences.

Why (C) is correct: In the resting state, the concentration of Na⁺ ions is significantly higher outside the neural membrane than inside. Therefore, if diffusion were the only force acting, Na⁺ would naturally move into the cell down its concentration gradient.

Why other options are wrong:

• (A) K⁺ into the cell: K⁺ concentration is higher inside the cell, so diffusion would drive it out, not in.
• (B) K⁺ and Na⁺ out of the cell: Na⁺ would move in, not out, due to its concentration gradient.
• (D) Na⁺ out of the cell: Na⁺ concentration is higher outside, so it would move into the cell, not out.

Common Mistake: Students often confuse the direction of ion movement due to concentration gradients with the active transport by the Na⁺/K⁺ pump, which works against these gradients.

NEET Tip / Mnemonic: Remember "Na-Out, K-In" for the resting state's concentration gradients (Na⁺ high outside, K⁺ high inside). Diffusion always tries to equalize these, so Na⁺ wants to rush in, and K⁺ wants to rush out.

Correct Answer: (C)