Slenn said:
The title says it all. What is the most toxic chemical you have handled. Just the other day I was using aqua regia to etch a vial, which is a 3:1 combo of hydrochloric acid and nitric acid. And I thought that it was the most hazardous thing I've ever used. Although, the liquid nitrogen for physics demos would be another compound that could've been equally as dangerous.
tox·in   /ˈtɒksɪn/ Show Spelled
[tok-sin] Show IPA
?noun
any poison produced by an organism, characterized by antigenicity in certain animals and high molecular weight, and including the bacterial toxins that are the causative agents of tetanus, diphtheria, etc., and such plant and animal toxins as ricin and snake venom.
I know it's nitpicky for me to do this, but since this is a sciencey sort of question, I thought that it might be a good idea for the question to be worded in a more accurate way, and "toxic" isn't really the best choice here.