How does atomic size of elements vary on moving from top to bottom in a group

Explanation

(a) Atomic size goes on decreasing from left to right because one proton and one electron is being added successively therefore, force of attraction between valence electrons and nucleus increases therefore, atomic size decreases.
(b) The atomic size goes on increasing from top to bottom in a group because number of .shells keep on increasing .therefore, distance between nucleus and valence electrons increases.