Final answer:
The initial rate the nurse should set the intravenous pump for the prescribed insulin solution is 1 unit per hour.
Step-by-step explanation:
To calculate the initial rate the nurse should set the intravenous pump, we need to divide the number of units prescribed by the perinatologist by the total volume of the solution. In this case, the perinatologist prescribed 25 units of insulin in 250mL of normal saline. Therefore, the initial rate should be 1 unit per hour (25 units ÷ 250mL = 0.1 units/mL x 10 mL/hour = 1 unit/hour).