How many electrons can occupy the first electron shell?

• A. 2 Electrons
• B. 1 Electron
• C. 8 Electrons
• D. 4 Electrons

Answer: (A)

The main idea here is how electrons are arranged in atomic shells. The first shell (n = 1) has only one sublevel, the 1s, which contains a single orbital. A single orbital can hold two electrons, provided they have opposite spins, due to the Pauli exclusion principle. Therefore, the first shell can hold a maximum of two electrons. The other options don’t fit because one electron would leave the 1s orbital incomplete, eight electrons would require filling the second shell’s orbitals (2s and 2p), and four electrons would imply more than the first shell can accommodate. So two electrons is the correct limit.