I Think the most dangerous is hydrogen because its hightly inflamable and u can have hydrogen Bomb but a nuclear bomb use uranium and plutonium ...

plus, plutonium all by itself sitting on a bench can flat out kill you.

Uranium too, really.

Probably one of those crazy unstable isotopes would be the mostest dangerous.

Google says plutonium.

The human brain.

either hydrogen / helium since most of the universe is made out of it.

Carbon of course.
Btw, wtf is helium doing on there? That has to be like the least dangerous element of all...

Where is ionized Florine!?

I seriously am taken aback to anything that can bond with things that are noble.

id say cesium

uranium is not particular harmful until humans do a shit ton of stuff to it, including filtering all the non radioactive uraniums and sticking all the radioactive uranium molecs together, then blasting neutrons at it till it flies apart making all the rest of the uranium molecules in that clump blast apart. WHICH in turn can create enough heat and pressure to fuse small atoms into bigger ones. ONLY THEN does it really become a problem

Helium makes you talk like a little girl so clearly it must frighten you. Obviously that has to be the most dangerous
Or maybe it'd be Hydrogen I think, since it has the highest potential energy jump to Helium.

plutonium i would have to say.