Regions of space around the nucleus that can hold up to two electrons and have shapes designated by letters are called

• A. Electron shells
• B. Atomic orbitals
• C. Subshells
• D. Molecular orbitals

Answer: (B)

Atomic orbitals are the regions of space around the nucleus where electrons are most likely to be found. Each orbital can hold up to two electrons with opposite spins, which comes from the Pauli exclusion principle. The shapes of these regions are labeled by letters—s, p, d, f—reflecting their angular momentum and orientation, from the spherical s to the dumbbell-shaped p and beyond. This is distinct from electron shells, which are the overall energy levels that can contain many electrons, and from subshells, which are groups of orbitals within a shell that share the same n and l values. Molecular orbitals, on the other hand, are spread over a molecule rather than a single nucleus. The description given—regions around the nucleus that hold two electrons and have shapes designated by letters—matches atomic orbitals.