What is the maximum number of electrons that can occupy the first shell of an atom?

The first shell of an atom, also known as the K shell, is governed by the principles of quantum mechanics and can hold a maximum of two electrons. This limitation arises from the Pauli exclusion principle, which states that no two electrons can occupy the same quantum state simultaneously. The first shell corresponds to the principal quantum number n=1, and it contains only one subshell (the s subshell) that can hold only two electrons with opposite spins. Therefore, the maximum occupancy of the first shell is correctly identified as two electrons, making it essential for understanding atomic structure and the behavior of elements in chemistry and physics.