Drag and drop with only one element on the hotspot

I'm trying to build an exercise where the user shall drop several items on several hotspots. It shall only be possible to have one item on each hotspot a time but the user shall be able to try different solutions. I achiveved this by transforming the slide to a drag and drop question, but then I got limited to one correct drop target for each object

Is there any way  to limit the drag and rop to one object on each target, but letting it be possible to drop the objects on several different positions?

Also, Is it possible to make the object return to the position it was dragged from instead of to the original position of the drop is not allowed?

Finally, if there is any way to find out if a drop target has any object attached or not (and if so, which object) and put that info in a varaiable it would really simplify constructing the logic behind the exercise.