Answer:
Option C:
1s2 2s2 2p6 3s1 3p4
Explanation:
At a ground level, Phosphorous has an electronic configuration of 1s2 2s2 2p6 3s2 3p3 (using the spdf notation).
Once the atom becomes excited, an electron from the 3s sub-level will gain energy and jump over to the 3p sub-level, making the configuration 1s2 2s2 2p6 3s1 3p4.
The number of electrons at the 3p sub-level will now become 4 because of the addition of the new electron while the number of atoms at the 3S sub-level will reduce to 1 because an electron left this sub-level.
