Which of the following cannot be polarised?

The wavelength of sound waves in hydrogen gas corresponding to the lower limit of audibility is ........ $m$ (speed of sound in hydrogen gas is about $1350 \, m/s$).

What is the ratio of the velocity of sound in hydrogen $\left(\gamma=\frac{7}{5}\right)$ to that in helium $\left(\gamma=\frac{5}{3}\right)$ at the same temperature? (Molecular weight of hydrogen and helium is $2$ and $4$ respectively)

Find the frequency of the minimum distance between a compression and a rarefaction of a wire. If the length of the wire is $1\, m$ and the velocity of sound in air is $360\, m/s$,find the frequency in $sec^{-1}$.

The intensity of sound increases at night due to

The speed of sound in air at temperature $T$ and pressure $p$ is $v$. When the temperature is increased to $2 T$ and the pressure is reduced to $\frac{p}{2}$, then the speed is changed to