Final answer:
The highest occupied energy level in an atom of strontium in its ground state is n = 5, as indicated by its electron configuration which ends with 5s2.
Step-by-step explanation:
The highest occupied energy level in an atom of strontium in its ground state is the n = 5 level. Strontium has an atomic number of 38, which means it has 38 protons and, in a neutral atom, 38 electrons.
The electron configuration of strontium ends with 5s2, indicating that the outermost electrons occupy the 5s orbital, making n = 5 the highest energy level with electrons in the ground state.