Out of hot moist air and dry cold air,in which does sound travel faster?

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:

Regarding the speed of sound in a gas, match the following:

$A$. Temperature of gas is made $4$ times and pressure $2$ times	$P$. Speed becomes $2\sqrt{2}$ times
$B$. Only pressure is made $4$ times without change in temperature	$Q$. Speed becomes $2$ times
$C$. Only temperature is changed to $4$ times	$R$. Speed remains unchanged
$D$. Molecular mass of the gas is made $4$ times	$S$. Speed becomes half

Which of the following frequencies of sound waves is audible to human beings?

Write the displacement variable in the propagation of sound in air.

In a medium,sound travels $2 \, km$ in $3 \, sec$ and in air,it travels $3 \, km$ in $10 \, sec$. The ratio of the wavelengths of sound in the two media is