If 20 compressions pass a point in 4 seconds, the frequency is:

(a) 80 Hz

(b) 5 Hz

(c) 10 Hz

(d) 0.2 Hz

(b) 5 Hz

Explanation: Frequency is the number of oscillations (or compressions) passing a point per unit time. It is calculated as:

$$\text{Frequency} = \frac{\text{Number of compressions}}{\text{Time taken}}$$

$$= \frac{20}{4} = 5 \text{ Hz}$$

Hence, the frequency of the sound wave is 5 Hz.