Answer
See the answer below.
Work Step by Step
Radius increases from right to left and top down in the periodic table, so
a) $F(G17, P2)\lt O(G16, P2)\lt S(G16, P3)$
Ionization energy increases from left to right and bottom up in the periodic table, so
b) S, S and Se are in group 16 vs 15 for P and 14 for Si, but S is in the third period, vs fourth for Se.
d) $Cs(G1, P6)\lt Ba(G2, P6)\lt Sr(G2, P5)$
Radius is bigger in more negatively charged ions, so
c) $N^{3-}$
