Question on momentum

If you imagine say, runner 1 running at someone, say runner 2 whose running in the opposite direction at half the speed, it would make sense that the one who rebounds with a greater speed would be in the direction of the one running the fastest?

The answer is C. But why is option D incorrect? For elastic collision, isn't the relative speed of separation equal to relative speed of approach in D? Am I missing something?

I think you have made some mistakes in using the relative speed approach.

If you compute the overall "net" momentum before the collision, you should find 2m N s to the right where m is the mass of sphere.

From conservation of linear momentum, after the collision, the system should still have 2m N s to right.

Option D has a "net" momentum of 2m N s (to the left) after the collision.