Which of these chemicals is the most toxic?

You can not tell from the name or even personal experience. On the MSDS, you look for the LD50 and LC50 and LD100 and LC100 values. But make sure you compare apples and apples. An LD50 for a mouse is not comparable to a rat LD50. It also makes a difference what your definition of "toxic" entails. For example, methylene chloride is going to be a long term ingested toxin, while glacial acetic acid will rip your throat out swallowing it. However, just breathing the fumes from a beaker, methylene chloride is worse because it is more volatile. So you have to define "toxic" when you make these comparisons and you have to also compare equal doses and like exposures under exact conditions (temperature for example). You also run into trouble when you talk humans, since we don't test humans and the toxicity to humans is less than to rats and mice. Pigs are closer to humans.