Which is an example of a highly polar covalent bond. Ca - Cl Fe - O H - S F - F

For this you will need electronegativity (χ). χ (Ca) = 1, χ (Cl) = 3, χ (Fe) = 1,8, χ (O) = 3,5, χ (H) = 2,1, χ (S) = 2,5, χ (F) = 4. then you calculate difference of electronegativity between 2 atoms, where is highest, that is higly polar bond. So it is Ca-O bond Δ χ=2.