Step-by-step explanation:
Valence electrons are the electrons which are present in the outer most shell of an atom or element.
Since both potassium and sodium are same group elements and it is known that elements of same group contain same number of valence electrons.
For example, atomic number of potassium is 19 and its electronic distribution is 2, 8, 8, 1.
Hence, we can conclude that there is one valence electron present in valence shell of potassium atom.