Which would occur if a ball x were rolled across a smooth floor to collide with a similar ball y that was stationary

For a collision where objects will be moving in 2 dimensions (e.g. x and y), the momentum will be conserved in each direction independently (as long as there's no external impulse in that direction). In other words, the total momentum in the x direction will be the same before and after the collision.

Explanation:

you didnt put any of the following

catya your not at all which answer i've seen you do this on another question!