Answer:
B. Having the same number of valence electrons in their outer energy levels.
Explanation:
We are given that elements on the periodic table are arranged in groups because they have similar properties.
We have to fill the blank space.
Elements on the periodic table are arranged in groups because they have similar properties.
The elements have similar properties because they have same number of electrons in their outer energy level.
Therefore, these similar properties are the result of having the same number of valence electrons in the outer most shell.
Therefore, option B is true.
