Concept: This question tests your understanding of different types of membrane transport, specifically focusing on the mechanism of the ${\mathrm{Na}}^{+}/{\mathrm{K}}^{+}$ pump.

Why (A) is correct: The ${\mathrm{Na}}^{+}/{\mathrm{K}}^{+}$ pump moves ${\mathrm{Na}}^{+}$ ions out of the cell and ${\mathrm{K}}^{+}$ ions into the cell, both against their respective electrochemical gradients. This process requires energy, which is supplied by the hydrolysis of ATP. Any transport that requires metabolic energy to move substances against their concentration or electrochemical gradient is termed active transport.

Why other options are wrong:

• (B) passive transport: Passive transport does not require metabolic energy and moves substances down their concentration gradient.
• (C) osmosis: Osmosis is the movement of water across a semipermeable membrane, not ions.
• (D) simple diffusion: Simple diffusion is the passive movement of substances directly across the membrane down their concentration gradient, without the help of transport proteins or energy.

Common Mistake: Students sometimes confuse facilitated diffusion (which uses proteins but is passive) with active transport because both involve transport proteins.

NEET Tip: Remember that 'active' means 'requires energy (ATP)' and 'against gradient'.

Correct Answer: (A)