Answer: 2. The outermost shell
Step-by-step explanation:
In an elements ground state, its electrons have the least amount of energy that they could have so they stay in their shells. When Krypton is in this state therefore, its valence electrons will stay in the outermost shell.
As Krypton has a total of 36 electrons in this state, there will be 8 valence electrons and they will all be in the outer shell.