Answer is: greatest difference in electronegativity.
a) Δelectronegativity (Ca-Cl) = 3,16 - 1 = 2,16.
b) Δelectronegativity (H-Cl) = 3,16 - 2,2 = 0,96.
c) Δelectronegativity (Fe-Cl) = 2,2 - 1,83 = 0,37.
d) Δelectronegativity (P-Cl) = 3,16 - 2,19 = 0,97.
Molecule that has difference in electronegativity greater than 1,7 is with ionic bond and less than 1,7 is covalent molecule.
