I'm not going to say that I have any knowledge of chemistry, because I don't. That being said, I did made some research on the subject since this character's abilities are abilities that I've used in many many characters. Sulfuric acid, when mixed with water, is able to completely dissolve skin and tissue in about 12 hours, and in 2 days, the bones will also have melted. This is the acidity that I would like to have on my character.