Potassium (k): 1s22s22p63s23p64s1 core electrons and valence electrons

An atom of potassium contains 18 core electrons and 1 valence electrons.

Explanation:

Core electrons are defined as the electrons which are present in the inner shells of an atom.

Valence electrons are defined as the electrons which are present in the outermost shell of the atom.

For the given electronic configuration of potassium (K):

The outermost shell of this configuration is '4s' and rest are considered as inner shells.

Thus, an atom of potassium contains 18 core electrons and 1 valence electrons.