Out of Sr, Ca, As, N, which element has the smallest atomic radius?

The answer is $N$. Why?
We have Period 5 $S r$, and Period 4 $C a$, both metals to the left hand side of the Table, and Period 4 $A s$. Arsenic is without doubt the smallest of these atoms. But arsenic is without doubt LARGER than nitrogen, which is a 2nd Period atom to the right of the Periodic Table.