When we close **or** flag a question as *off-topic*, we have an option called `belongs to meta.physics.SE`. We're also receiving questions that belong to Math.SE or Electronics.SE most of the time. So, it'd be easy for migration if there is a choice for `belongs to Math.SE` and `belongs to Electronics.SE`. Well, other sites do have that option. For instance, we can take Android.SE. It's having a choice for `belongs to SO`. I think superuser is also having such an option. 