When a tuning fork produces sound waves in air,which one of the following remains the same in the material of the tuning fork as well as in the air?

$P$ and $Q$ are two wires whose fundamental frequencies are $256 \ Hz$ and $382 \ Hz$ respectively. How many beats per second will be heard if the third harmonic of $P$ and the second harmonic of $Q$ are sounded together?

$A$ tuning fork $A$ produces $4$ beats/sec with another tuning fork $B$ of frequency $320 \text{ Hz}$. On filing the fork $A$,$4$ beats/sec are again heard. The frequency of fork $A$ after filing is .... $\text{Hz}$

$A$ set of $20$ tuning forks is arranged in a series of increasing frequencies. If each fork gives $4 \; Hz$ beats with respect to the preceding fork and the frequency of the last fork is twice the frequency of the first,then the frequency of the last fork is $\dots \; Hz$.

When temperature increases,the frequency of a tuning fork

Two vibrating strings $A$ and $B$ produce beats of frequency $8 \ Hz$. The beat frequency is found to reduce to $4 \ Hz$ if the tension in the string $A$ is slightly reduced. If the original frequency of $A$ is $320 \ Hz$, then the frequency of $B$ is: (in $Hz$)