Two particles $A$ and $B$,initially at rest,move towards each other under a mutual force of attraction. At an instance when the speed of $A$ is $v$ and the speed of $B$ is $2v$,the speed of the centre of mass $(CM)$ is:

A prism of angle $75^\circ$ and refractive index $\sqrt{3}$ is coated with thin film of refractive index $1.5$ only at the back exit surface. To have total internal reflection at the back exit surface the incident angle must be . . . . . . .
$(\sin 15^\circ = 0.25$ and $\sin 25^\circ = 0.43)$

Genus represents

The circuit given below is that of:

Beryllium is placed above magnesium in Group $2$. What happens when beryllium powder is added to a solution of $MgCl_2$?

When ethanol is reacted with $PCl_5$,it gives $A$,$POCl_3$,and $HCl$. The reaction of $A$ with silver nitrite $(AgNO_2)$ gives the major product $(B)$ and $AgCl$. What are $A$ and $B$ respectively?