This question is about momentum conservation, which belong to physics subject.
You start by assuming that the friction coefficient of bwtween the roller skates and the ice is very low and think there is not friction.
Under those circumstances the convservation of momentum implies:
1) When the roller skater throws the 2 kg balls, it will acquire a momentum equal to v*2kg and the skater will acquire equal momentum in the opposite direction.
That means that the skater will step back and away from the other skater.
2) When the second skater receives the ball with momentum 2kg*v, he will move backward also and further away.
In conclusion, the two skaters will end standing more than 5 m apart facing each other.
there is 8 atoms of Carbon.