The sodium-potassium pump can transport the sodium-potassium pump can transport only if sodium and potassium are available sodium even if potassium is not available potassium even if sodium is not available sodium even if potassium is not available and potassium even if sodium is not available

The correct answer is: only if sodium and potassium are available.

The sodium-potassium pump is an enzyme that uses the chemical energy stored in ATP molecules to export 3 sodium ions out of the cell and to import 2 potassium ions into the cell. This happens simultaneously, so the presence of both of the ions is necessary.  

Active site is where they touch.