Step-by-step Solution:

We know that frequency is defined as the number of cycles in one second.
Given:
Number of cycles in 1 second = 2500 million
Therefore, $$ \text{Frequency} = 2500\ \text{MHz} $$ We also know that time period (T) is the inverse of frequency and is defined as the time taken for one cycle: $$ T = \frac{1}{F} $$ Substituting the value: $$ T = \frac{1}{2500 \times 10^6} $$ $$ T = 4 \times 10^{-10} \ \text{seconds} $$