Tow particles `X` and `Y`, of equal mass and with unequal positive charges , are free to move and are initially far away from each other . With `Y` at rest , `X` begins to move towards it with initial velocity `u`. After a long time , finally .

Answer

A

Explanation

Equal electrostatic force (mutual interaction) acts on X and Y but in opposite direction which accelerate Y but retards X. After long time the velocity of X becomes zero while Y becomes u.