How many electrons are contained in an ion formed from an atom of K?

Potassium (K) is an alkali metal whose atoms have one valence electron. The atomic number of K is 19, which means its atoms have 19 protons in their nuclei. A neutral K atom also has 19 electrons. An atom of K will lose its single valence electron to become a K+ cation. Therefore, there are 18 electrons in a K+ cation.