Answer:
Sodium
Explanation:
This would leave you with 3 shells of 2, 8, and 1. Since it has one more shell then the second shell has to be 8. Since the first shell can only contain up to 2 it must be 2/8. And since it has one less valence electron than beryllium it must be a config of 2/8 1, which is the electron config of Sodium, Element with Atomic number 11 and electron shell of 2/8 1.
