Knock-knock. Who's there? To. To who? No, to whom.
Q: What happened to the man who was stopped for having sodium chloride and a nine-volt in his car? A: He was booked for a salt and battery.
Q: Why can't you tell blondes knock-knock jokes? A: Because they leave to go answer the door.
Q: Anyone know any jokes about sodium? A: Na
Knock Knock. Who's there? Opportunity. Don't be silly - opportunity doesn't knock twice!
Q: What do you call a tooth in a glass of water? A: One molar solution.
Fast way to screw up someone's Knock Knock joke...? "It's open."
Q: Why was the mole of oxygen molecules excited when he walked out of the singles bar? A: He got Avogadro's number!
Knock knock. Who's there? Sarah. Sarah who? Sarah problem here?
Knock Knock. Who's there! Ice cream! Ice cream who? Ice cream if you don't let me in!
"Knock, knock.Who's there?" very long pause... "Java."