The product is:

Consider the following statements $A$ and $B$ and identify the correct answer.
$A$. In an elastic collision,if a body suffers a head-on collision with another of the same mass at rest,then the first body comes to rest while the other starts moving with the velocity of the first one.
$B$. Two bodies of equal mass suffering a head-on elastic collision merely exchange their velocities.

How many unit cells are present in $39 \ g$ of potassium that crystallises in body-centred cubic structure? [At. wt. of $K = 39$]

Suppose $A$ and $B$ are two points on the line $2x-y+3=0$ and $P(1,2)$ is a point such that $PA=PB$. Then,the mid-point of $AB$ is

$z=\tan (y+a x)+\sqrt{y-a x} \Rightarrow z_{x x}-a^2 z_{y y}$ is equal to

Amongst $LiCl$,$RbCl$,$BeCl_{2}$,and $MgCl_{2}$,the compounds with the greatest and the least ionic character,respectively,are