You simply say OBJECT on collision with PLAYER >> spawn your explosion, add your score, then OBJECT destroy
and that should destroy only the object that collided
Another tip that you might need, there is a SYSTEM select random instance which is useful to pick one out of many instances.
Another possibility is to put a condition to OBJECT that OVERLAPS the player, which will then only apply to those specific instances which are overlapping. This is useful if you have for example a planet that has an atmosphere and if a plane flies out then it would be destroyed via NOT overlapping atmosphere.