Velocity of sound in vacuum is .... $ms^{-1}$

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: $A$ sound wave has higher speed in solids than gases.
Reason $R$: Gases have higher value of Bulk modulus than solids.
In the light of the above statements,choose the correct answer from the options given below:

For a particular sound wave propagating in air, a path difference between two points is $0.54 \, m$ which is equivalent to a phase difference of $(1.8 \pi)$. If the velocity of the sound wave in air is $330 \, m/s$, the frequency of this wave is: (in $Hz$.)

$v_1$ and $v_2$ are the velocities of sound at the same temperature in two monoatomic gases of densities $\rho_1$ and $\rho_2$ respectively. If $\frac{\rho_1}{\rho_2} = \frac{1}{4}$,then the ratio of velocities $v_1$ and $v_2$ will be

Which of the following is not a transverse wave?

When a tuning fork vibrates,the waves produced in the fork are