Physics - Sound Wave Question with Solution | TestHub

Since $\mathrm{A}$ produces four beats with $\mathrm{B}$.
So, frequency of $\mathrm{B}$ could be $260 \mathrm{Hz}$ or $252 \mathrm{Hz}$.
After waxing, frequency decreases. So, frequency of $\mathrm{B}$ has to be less than $256 \mathrm{Hz}$ as it produces same number of beats with $\mathrm{A}$.

So, the frequency of $\mathrm{B}$ is $252 \mathrm{Hz}$..