Correct option (d) \(508 \mathrm{~Hz}\)
Explanation:
Let the frequencies of tuning fork and piano string be \(v_{1}\) and \(v_{2}\) respectively.
Increase in the tension of a piano string increases its frequency.
If \(v_{2}=508 \mathrm{~Hz}\), further increase in \(v_{2}\) resulted in an increase in the beat frequency. But this is not given in the question. \(508 \mathrm{~Hz}\). further increase in \(\mathrm{v}_{2}\) resulted in decrease in the beat frequency. This is given in the question" When the beat frequency decreases to 2 beats per second. Therefore, the frequency of the piano string before increasing the tension was \(508 \mathrm{~Hz}\).
