Answer: option (a) is the correct answer.
Step-by-step explanation:
In a periodic table, when we move from top to bottom in a periodic table then there will be increase in number of shells because of addition of more number of electrons.
As a result, there will be increase in atomic radius of the atom.
Metals are the elements which have excess of electrons but on moving from left to right in a periodic table reactivity of metals decreases as there valence shells does not contain extra electrons to donate.
On the other hand reactivity of non-metals increases on moving from left to right.
Hence, we can conclude that the statement atomic radius increases moving down a column, is true about the periodic table.