What element is represented #[Kr]5s^1#?
Well if it's a neutral element, the element is
Look at a copy of the the Periodic Table, and look at the 4th and 5th Periods. Krypton is an inert gas that ends a Period; rubidium is an alkali metal that begins the next Period, the 5th Period.
In practice, we don't even have to know about electronic configuration.