Which of the following principles is being used in $SONAR$ technology?

Obtain the equation for the speed of a sound wave in air and identify the error in this equation.

$A$ mechanical wave (sound wave) in a gas is:

The speed of sound in mercury at a certain temperature is $1450 \, m/s$. Given the density of mercury as $13.6 \times 10^3 \, kg/m^3$,the bulk modulus for mercury is:

$A$ string is stretched so that its length is increased by $\frac{1}{\eta }$ of its original length. The ratio of the fundamental frequency of transverse vibration to that of the fundamental frequency of longitudinal vibration will be

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