How many places are there for electrons in the innermost shell of an atom? A. 2 B. 4 C. 8 D. 12

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 (n2) electrons.