Which kinds of objects emit visible light in the electromagnetic spectrum? 1)all objects2)radioactive objects3)relatively cold objects4)relatively hot objects

Relatively hot objects emit visible light.
Some examples: 
==> the wire coils in the toaster; 
==> the spoon that you stuck in the flame on the stove;
==> the fine wire in the lightbulb when current goes through it.

VERY radioactive objects also do that.  But if you're actually
standing there watching an object that's THAT radioactive,
then you're in big trouble.