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.

consider the reaction below.

 no rx

at 500 k, the reaction is at equilibrium with the following concentrations.

[pci5]= 0.0095 m

[pci3] = 0.020

[ci2] = 0.020 m

what is the equilibrium constant for the given reaction?

0.042

0.42

2.4

24