If refractory period of nerve is 1/2500th of a second, what can be the maximum frequency of excitation of the nerve?

Refractory period is that time period after the first stimulus during which the nerve is "refractory" to another stimulus. Hence, maximum frequency of excitation can be 2500 times in a second, as each next stimulus can excite the nerve if applied immediately at the end of the refractory period (1/2500th of a second).