What element has the symbol 'I'?

The story behind the answer

Iodine has the chemical symbol I. Among the choices, the others differ: Indium is In, Iridium is Ir, and Iron is Fe (from Latin ferrum). So the single-letter I points uniquely to iodine.

Iodine (atomic number 53) is a halogen known for its deep-violet vapor when heated—its name comes from the Greek ioeides, meaning “violet-like.” It’s essential for thyroid hormones, which is why table salt is often iodized. Memory hook: “I is Iodine’s Indigo vapor,” while Iron’s Fe reminds you of ferrum, and the other I-elements need two letters—In for