The period is the time taken by the wave to complete an oscillation. The frequency of the given sound is 500 Hz.
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Period:</h2>
It is the time taken by the wave to complete an oscillation. The frequency is inversely proportional to the time:

Where,
- frequency
- period = 0.002 s
Put the value in the equation,

Therefore, the frequency of the given sound is 500 Hz.
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The answer is B, or endoplasmic reticulum.