Amongst isoelectronic species, smaller the positive charge on the cation, smaller is the ionic radius.

Amongst isoelectronic species, greater the negative charge on the anion, larger is the ionic radius.

Atomic radius of the elements increases as one moves down the first group of the periodic table.

Atomic radius of the elements decreases as one moves across from left to right in the 2^nd period of the periodic table.

$$-$$ 5.1 eV

$$-$$ 10.2 eV

+2.55 eV

+10.2 eV

Mg < Ca < Cl < P

Cl < P < Mg < Ca

P < Cl < Ca < Mg

Ca < Mg < P < Cl

CsI

CsF

LiF

NaF