1. Find Strontium on the Periodic Table:
* Strontium is in Period 5, Group 2 (alkaline earth metals).
2. Identify the Preceding Noble Gas:
* The noble gas that comes before strontium is krypton (Kr), which is in Period 4.
3. Determine the Remaining Electrons:
* Strontium has an atomic number of 38, meaning it has 38 electrons.
* Krypton has an atomic number of 36, meaning it has 36 electrons.
* This means strontium has 2 additional electrons beyond krypton's configuration.
4. Write the Noble Gas Configuration:
* The correct noble gas configuration for strontium is [Kr] 5s².
Therefore, the correct answer is [Kr] 5s².
