Two identical balls bearing in contact with each other and resting on a frictionless table are hit head on by another ball bearing the same mass moving initially with a speed v as shown in figure. If the collision is elastic, which of the following (figure) is a possible result after collision? [NCERT Exemplar]

When two bodies of equal masses collide elastically, their velocities are interchanged.When ball 1 collides with ball 2, then velocity of ball 1, v1becomes zero and velocity of ball 2, v2 becomes v, i.e.                          v1 = 0  and v2 = vSimilarly, when ball 2 collides with ball 3 , v2 = 0 and v3 = v.Also in elastic collision both momentum and energy remain conserved .Hence, figure (2) is correct.