Bad water pollution with radionuclides. Fishing might have to be banned. Possibly radioactive rain and snow, depending on how deep or shallow they exploded.
No nuclear energy, no nuclear weapons
To the planet very little. To life an awful lot.
Nothing
That depends on whose wrong hands.
Some one would invent them
Not very likely countries as are now getting rid of their nuclear weapons to aviod a nuclear war
the world will blow up
If a nuclear missile detonated on the Ring of Fire, it could potentially trigger seismic activity, tsunamis, and volcanic eruptions due to the region's already active tectonic plates. The consequences could be catastrophic for the surrounding countries and have far-reaching environmental impacts.
Not bloody likely! It means nations destroy their nuclear weapons, quit making anymore, and all somehow forget how they are made. But as there are no real secrets about making them, that isn't gonna happen.
No one has actually tried this before, and no physics engine has ever managed to imitate effects of such great force, so therefore it is quite hard to answer this question.
Yes! A nuclear weapon (especially a small one (as much as small can be applied to nuclear weapons)) can miss enough to render the weapon tactically ineffective. This could happen with ICMS if the guidance system failed, sending the weapons (in a MIRV) into the ocean, or onto a remote piece of land.
Atlantis Underwater Tycoon happened in 2003.