Which substance is used as a gaseous insulator in high-voltage generators?

Which of the following is a scalar quantity?

$A$ musical instrument $P$ produces sound waves of frequency $n$ and amplitude $A_P$. Another musical instrument $Q$ produces sound waves of frequency $\frac{n}{4}$. The waves produced by $P$ and $Q$ have equal energies. If the amplitude of waves produced by $P$ is $A_P$,the amplitude of waves produced by $Q$ will be: (in $A_P$)

$A$ disc is rotating with an angular velocity $\omega_0$. $A$ constant retarding torque is applied on it to stop the disc. The angular velocity becomes $(\omega_0/2)$ after $n$ rotations. How many more rotations will it make before coming to rest?

The point on the line $3x + 4y = 5$ which is equidistant from $(1, 2)$ and $(3, 4)$ is

In the Liebermann's nitroso reaction,the sequential changes in the colour of phenol occur as: