Provide your best answer for the following question. Give ONLY the answer, no other words or explanation.
For example:

Answer: <most likely answer, as short as possible; not a complete sentence, just the answer!>.

The question is: The element cesium, Cs, is an alkali metal. Which chemical formula represents a cesium compound that is likely to exist?
CsCl, CsBr, or CsI. (Any one of these answers is acceptable.)