Which are the main radioactive elements around us?

It depends on where you are. Here radioactive elements aka (uranium is plentiful here) form radon gas which is dense and therefore tends to accumulate in valleys that's why I live atop a big hill.

Edited December 6, 201510 yr by fiveworlds

There are two radioactive isotopes that are inside you. But people shouldn't just be giving out answers. What have you done so far to answer this?

There are two radioactive isotopes that are inside you. But people shouldn't just be giving out answers. What have you done so far to answer this?

There are more than 2.

Also, if Fiveworlds thinks that dense gases accumulate in valleys to any meaningful extent, how does he explain that the people in these valleys don't die from CO2 poisoning.

 

Perhaps he missed science 101; the properties of gases.

http://www.bbc.co.uk/bitesize/ks3/science/chemical_material_behaviour/particle_model/revision/4/

 

Property of gases :

They flow and completely fill their container.

Fair enough. Two prominent ones.