Question

symbol 1 *
choose
single electron
pair of electrons with opposite spins
atomic orbital (region of space where an electron is likely to be found)
sublevel (set of orbitals having equivalent energy)
electron configuration

Explanation:

In chemistry, a box in orbital - filling diagrams represents an atomic orbital, which is the region of space where an electron is likely to be found.

Answer:

Atomic Orbital (region of space where an electron is likely to be found)