[William D]

Which atom in each group "I" and "II" has the smallest atomic radius?

(Group I) Sr, Zr, I

(Group II) N, P, As

 Sr and N
 Sr and As
 I and N
 I and As

[Astrokel]

Generally, the atomis radius increases down the group and decreases then increases across period.

[gingerbread_girl]

Hey i read this and the answer is that atomic radius increases down a group and across a period in the periodic table. That ought to help

[tamim83]

Atomic radius decreases across a period due to increasing effective nuclear charge.  This is only in the main group elements; transition metals have very similar atomic radii.