How many electrons can the first electron shell hold at maximum?

The first electron shell, also known as the K shell, can hold a maximum of two electrons. This is determined by the formula 2n², where n represents the principal quantum number of the shell. For the first shell, n is 1, so plugging that into the formula gives 2(1)² = 2.

This limitation is due to the physical and energetic constraints of the electrons in their lowest energy levels, which allows only for a pairing of electrons with opposite spins in each orbital of the shell. Thus, at maximum capacity, this shell is completely filled with two electrons.