What makes the atomic radius change down a column of the periodic table?

“When we move down a group then there is increase in the size of elements because there occurs increase in atomic mass of the elements.
It means that there occurs increase in number of electrons due to which there will be increase in number of new shells. As a result, size of atom or element increases due to which there is increase in atomic radius of the element.
Therefore, we can conclude that increase in number of electrons makes the atomic radius change down a column of the periodic table.”

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