Depends on what it is choked.
Yes.
Yes: A Remington 870 shotgun with a modified choke will shoot any commercial shotgun slug.
Any non rifled slug. However for best perfomance you want a "saboted" slug.
Yes, but, DON'T DO IT!!!!!!!!
Yes, if it is a 10 gauge shotgun.
Yes
Do not try it, the likelihood of the gun exploding in your hands is very high.
no
The Stevens 59A can shoot all size loads from #12 to slug. So in short, yes.
As long as the owner's manual doesn't prohibit it.
Yes and no. The yes comes from simple fact, if the projectile can move down the barrel, it can be fired. I've seen .221 Fireballs fired out of a 7TCU barrel. The no is because you cannot do it well. In effect, if you shoot a slug down a smooth bore shotgun barrel, you will have little in the way of accuracy. Slugs should be shot from a slug barrel, and shot from a smooth bore.
Yes, you can shoot a slug in an Ithaca M66 Super Single shotgun, provided it has a smoothbore barrel. It's important to use the appropriate type of slug designed for smoothbore shotguns. Always ensure that the shotgun is in good condition and follow safety guidelines when using slugs, as they can produce more recoil than traditional shot loads.