Rulings

You exile an instant or sorcery spell you control from the stack, not an instant or sorcery card in any other zone.
Exiling a spell is not the same as countering it, although the spell won’t resolve in both cases. You may exile a spell that can’t be countered.
You can exile a copy of an instant or sorcery spell to activate Nivmagus Elemental’s ability if you control the copy.