Answer:
B.) 1s²2s²2p⁶3s¹
Explanation:
Sodium is the first element in the third period of the periodic table. Because it lies within the "s" block, the highest energy orbital should be an "s" orbital. Because sodium lies within the 3rd period, the highest energy orbital should be "3s". Because sodium is the first in the row, there is only one electron that can occupy the highest energy orbital. Therefore, the electron configuration of sodium is 1s²2s²2p⁶3s¹. No elements within the third period occupy a "d" orbital.
