Answer:
The correct option is: Potassium
Explanation:
Sodium, Potassium, Rubidium and Caesium are referred to as the alkali metals that belong to the group 1 of the periodic table, thus having one valence electron in their outer or valence shell.
Sodium, atomic number 11, belongs to the period 3 of the periodic table. It has three shells and the number of electrons per shell is 2, 8, 1.
Potassium, atomic number 19, belongs to the period 4 of the periodic table. It has four shells and the number of electrons per shell is 2, 8, 8, 1.
Rubidium, atomic number 37, belongs to the period 5 of the periodic table. It has five shells and the number of electrons per shell is 2, 8, 18, 8, 1.
Caesium, atomic number 37, belongs to the period 6 of the periodic table. It has six shells and the number of electrons per shell is 2, 8, 18, 18, 8, 1.
Therefore, Potassium, atomic number 19, has four shells or energy levels.
