Answer:
shells 1, 2 and 3 are full and shell 4 has one electron
Step-by-step explanation:
The distribution fo the electrons possessed by an atom in the shells surrounding it is termed as its electronic configuration.
According to the rules of writing the electronic configuration:
1. The first shell can be occupied by a maximum of two electrons.
2. the subsequent shells can be occupied by a maximum of 8 electrons.
3. the subsequent shells are filled only once the lower shells have been filled.
Based on these rules, the electronic configuration of potassium should be 2, 8, 8, 1. (2+8+8+1 = 19).
Thus, we can see that the first three shells are filled, and the last one has one electron left.