The correct order of atomic radii is:

As the number of electrons are increased it increases the radius of the element.  As the number of protons are increased the radius is decreased.

As we can see:

Radius of :

$$\begin{gathered} \mathrm{Eu}=199 \mathrm{pm} \\ \mathrm{Ce}=183 \mathrm{pm} \\ \mathrm{Ho}=176 \mathrm{pm} \\ \mathrm{N}=170 \mathrm{pm} \end{gathered}$$