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

Five identical springs are used in the following three configurations. The time periods of vertical oscillations in configurations $(i)$,$(ii)$ and $(iii)$ are in the ratio:

The equation of the circle concentric with the circle $x^2+y^2-6x+12y+15=0$ and having double its area is

The number of lone pairs of electrons present on $Xe$ in $XeF_4$ is

Which animal possesses neurons but lacks a brain?

Six identical conducting rods are joined as shown in the figure. Points $A$ and $D$ are maintained at temperatures $200\,^{\circ}C$ and $20\,^{\circ}C$,respectively. The temperature of junction $B$ will be ........ $^{\circ}C$.