Joke #399

Joke: What's Batman's favorite element?

Joke: Why can't you ask a chemist to make you a Pb and J sandwich?

Joke: What did the proton say to the other proton?

Joke: What do you call a secret agent compound?

Joke: Who is Iron Man interested in?

Joke: Knock knock!
Who's there?
Aldehyde!
Aldehyde who?
...
Must have been a leaving group.