What element has the symbol 'Kr'?

The story behind the answer

The symbol Kr stands for Krypton, a real chemical element (atomic number 36) in the noble gas group. The other options aren’t recognized elements. Like its noble gas neighbors (Ne, Ar, Xe), Krypton is colorless, odorless, and very unreactive.

Discovered in 1898 by Ramsay and Travers, its name comes from the Greek kryptos, meaning “hidden,” because it’s a rare trace in Earth’s atmosphere. Krypton is used in high-intensity lighting and camera flash lamps. Memory tip: think “Krypton is a noble gas, keeping reactions ‘kryptic’—so Kr for Krypton.” And while Superman’s home planet is Krypton, “kryptonite” isn’t an element—so stick with the real one: Krypton = Kr.