Final answer:
The electron configuration for an atom of phosphorus-31 in an excited state is [Ne] 3s2 3p3 4s2 3d6.
Step-by-step explanation:
The electron configuration for an atom of phosphorus-31 in an excited state is [Ne] 3s2 3p3 4s2 3d6.
In the ground state, the electron configuration of phosphorus is 1s2 2s2 2p6 3s2 3p3. To write the electron configuration of an excited state, we add the electrons to the appropriate energy levels and orbitals according to Hund's rule and the Aufbau principle.
This means that in the excited state, one electron from the 3p orbital has moved to the 4s orbital, and one electron from the 3s orbital has moved to the 3d orbital.