Answer:the frequency of the longitudinal wave is 200 Hz.
Explanation:The frequency of a wave is the number of complete cycles of the wave that occur in one second. In this case, the wave has 20 compression and 20 rarefaction in 0.1 second, which means it has completed 20 complete cycles in 0.1 second. Therefore, the frequency of the wave can be calculated as follows:
Frequency = Number of cycles / Time = 20 cycles / 0.1 s = 200 Hz
So, the frequency of the longitudinal wave is 200 Hz.