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

The first shell of an atom can hold a maximum of two electrons. This is based on the principles of quantum mechanics, specifically the arrangement of electrons in atomic orbitals. The first shell corresponds to the principal energy level n=1, which contains only one s subshell. The s subshell can accommodate a maximum of two electrons, each with opposite spins. This foundational concept is crucial for understanding the structure of atoms and how electrons are arranged around the nucleus. As shells increase in number, they can hold more electrons; however, the first shell is limited to just two.