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.
