What best explains the observed trend in atomic radii going down the periodic table

As we move from top to bottom, the y-value which is the Atomic Radii of the element tends to increase.

Explanation:

By adding more shells the atom gets bigger because  the electrons get further away creating more space, distance from the nucleus increases.

the answer is learned

since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.