Frequency \(\propto \sqrt{\text { Tension }}\)
If tension in \(B\) slightly decrease then frequency of \(B\) decrease.
If \(B\) is \(536 Hz\), as the frequency decreases, beats with A also decreases.
If \(B\) is \(524 Hz\), as the frequency decreases, beats with \(A\) increases.
\(\therefore\) Original frequency of \(B\) will be \(524 Hz\).