**Core Concept**
The refractory period is the time during which a nerve fiber cannot generate another action potential. In myelinated nerve fibers, the refractory period is divided into two parts: the absolute refractory period and the relative refractory period. The absolute refractory period is the time during which the nerve fiber is completely unable to generate an action potential, while the relative refractory period is the time during which the nerve fiber can generate an action potential, but only if the stimulus is strong enough.

**Why the Correct Answer is Right**
The refractory period is related to the time it takes for the voltage-gated sodium channels to recover from their activated state. The refractory period is typically measured as the time between the peak of one action potential and the peak of the next action potential. In myelinated nerve fibers, the refractory period is typically around 1-2 milliseconds. Given a refractory period of 1/2500 seconds, which is equivalent to 0.4 milliseconds, we can calculate the impulse rate using the formula: Impulse rate = 1 / (refractory period in seconds). This gives us an impulse rate of 1 / 0.0004 seconds = 2500 impulses per second.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not a valid impulse rate.
* **Option B:** This option is not a valid impulse rate.
* **Option C:** This option is not a valid impulse rate.

**Clinical Pearl / High-Yield Fact**
It's worth noting that myelinated nerve fibers have a faster conduction velocity and a shorter refractory period compared to unmyelinated nerve fibers. This is because the myelin sheath acts as an electrical insulator, allowing the action potential to jump from node to node, increasing the speed of conduction.

**Correct Answer:** D. 2500 impulses per second