This task can be easily done once we have the periodic table. From the periodic table, it can be seen that potassium is in the fourth row. Thus, it has four energy levels. If we are to use the same principle as that stated above, the number of energy levels for each are as follow:
Calcium = Ca (in periodic table) = energy levels
Iron = Fe (in periodic table) ; 4 energy levels
Nickel = Ni (in periodic table); 4 energy levels
Zinc = Zn (in periodic table) = 4 energy levels
