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.

it forms an anion that has a larger radius. anions have a negative charge and are larger than the original atom.