Use the chart to determine which pair of atoms has the greatest difference in electronegativity. A. Ca – Cl
B. H – Cl
C. Fe – Cl
D. P – Cl

A chart was not provided, but I believe that the answer would be A.

The electronegativity for chlorine is 3.2. Now, we must look for the electronegativity that has the greatest difference from chlorine.

Calcium (Ca) - 1.0
Hydrogen (H) - 2.2
Iron (Fe) - 1.8
Phosphorus (P) - 2.2

As you can see, the element with the lowest electronegativity level is Calcium, therefore the greatest difference in electronegativity would be present between Calcium and Chlorine.