When the ball on the left is pulled to the side and released, it will swing back due to gravity. Upon swinging back and colliding with the ball on the right, two metal balls of the same mass will transfer momentum upon impact.
Since both balls are of the same mass and the left ball is in motion while the right ball is at rest, the collision will result in the ball on the left stopping and the ball on the right gaining the kinetic energy of the left ball.
Thus, the correct conclusion is: The ball on the left will stop, and the ball on the right will swing to the right.