Choose the electron configurations which are possible for an unexcited atom. Example 1 – 1s22s22p4 Example 2 – 1s22s22p63s23p33d1 Example 3 – 1s22s22p83s1 Example 4 – 1s22s22p63s1

Examples 1, 3 and 4

Explanation:

An unexcited atom is an atom in the ground state i.e the atom has it's valence electrons in it's lowest energy level possible. This actually implies the normal electronic configuration of the atom. Thus, examples 1, 3 and 4 have the actual electronic configuration with there valence electrons in the lowest possible energy level.

Example 1: 1S² 2S² 2P⁴

Example 3: 1S² 2S² 2P⁶ 3S¹ (There seem to be a mistake in the question provided, P energy level can only 6 electrons not 8)

Example 4: 1S² 2S² 2P⁶ 3S¹

NOTE: If you take a look at example 2, it will be deduced that the 3P energy level has only 3 valence electrons and the last valence electron jumped to 3d energy level; making that atom appear to be in it's excited state.

the atomic number will stay the same no matter how many electrons it has, so it doesn’t decrease nor increase. it’ll only change with a different number of protons