What is the frequency of this wave?
1
2
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4

Answer: 2
Explanation:
Frequency can be defined as the number of oscillations or waves per second. It is measure in Hz.
1 Hz = 1 s⁻¹
In a longitudinal wave is the from one compression to another or one rarefaction to another. Here, there are 2 waves in 1 second. Thus, the frequency of the wave is 2 Hz.