What is the number of electrons in a completely filled second shell of an atom? (1) 32 (2) 2 (3) 18 (4) 8

Each shell can contain only a fixed number of electrons: The first shell can hold up to two electrons, the second shell can hold up to eight (2 + 6) electrons, the third shell can hold up to 18 (2 + 6 + 10) and so on. The general formula is that the nth shell can in principle hold up to 2 (n^2) electrons.

final answer: (4) 8 electrons

The second shell can only hold 2 electrons.

Final answer: 2 electrons