When two bodies collide elastically,then

Which one of the following statements does not hold good when two balls of masses $m_1$ and $m_2$ undergo elastic collision?

$A$ ball is thrown vertically downwards with velocity $\sqrt{2gh}$ from a height $h$. After colliding with the ground,it just reaches the starting point. The coefficient of restitution is:

After a head-on elastic collision between two balls of equal masses,one is observed to have a speed of $3\,m/s$ along the positive $x$-axis and the other has a speed of $2\,m/s$ along the negative $x$-axis. What were the original velocities of the balls?

$A$ moving body with mass $m_1$ strikes a stationary mass $m_2$. What should be the ratio $\frac{m_1}{m_2}$ so as to decrease the velocity of the first body by $1.5$ times after the collision?

$A$ particle of mass $m$ collides with another stationary particle of mass $M$. The particle $m$ stops just after the collision. The coefficient of restitution is: