The chemistry teacher was demonstrating the action of acids on various metals to his class.He dropped a 5 rupee coin into a glass of dilute acid and asked one of the students if the coin would dissolve.“No sir,” said the boy, “No chance!”“No?” said the teacher. “Perhaps you could explain to the class why the coin won’t dissolve?”“That’s easy, sir,” said the boy. “If it could dissolve you would never have dropped it in.”