False.
If a vial of 500,000 units of a medication is reconstituted with 4 mL, it will yield a concentration of 125,000 units/mL.
Concentration of a substance is calculated by dividing the number of units by the volume it occupies. In this case, the concentration of the medication would be 500,000 units / 4 mL = 125,000 units/mL.