Sodium-potassium pump and ion gradients Steps:

• Identify gradients: Na+ moves down from high outside to low inside (diffusion); K+ moves down from high inside to low outside (diffusion).
• Recognize pump function: Actively transports 3 Na+ out (against gradient) and 2 K+ in (against gradient) using ATP.
• Assign arrows based on direction: Arrow 1 shows Na+ entering (diffusion), 2 shows K+ entering (active), 3 shows Na+ exiting (active), 4 shows K+ exiting (diffusion).
• Match to choices: Only A correctly pairs these movements.

Why A is correct:

• A aligns with pump's exchange (active Na+ out via 3, active K+ in via 2) and diffusion down gradients (Na+ in via 1, K+ out via 4), per active transport definition.

Why the others are wrong:

• B: Swaps active transports, ignoring pump's directional exchange of Na+ out and K+ in.
• C: Misassigns diffusion of Na+ to 4 (outward, against gradient) instead of inward.
• D: Reverses active transports and K+ diffusion, contradicting ion concentrations.

Final answer: A