link between non-metal – non-metal is covalanet
then N-Cl will have the most covalent character
between Si and Fe….Fe is more metallic
so the covalent character will increase like this – F-Fe < Si-S < N-Cl edit - you gave me a thumbs up..... but I don't know why the electronegativity of Si = 1.9 electronegativity of S = 2.58 electronegativity of F = 3.98 electronegativity of Fe = 1.83 electronegativity of N = 3.04 electronegativity of Cl = 3.16 electronegativity difference between N-Cl = 3.16 - 3, 04 = 0.12 electronegativity difference between F-Fe = 3.98 - 1.83 = 2.15 electronegativity difference between Si- S = 2.58 - 1.9 = 0.68 because you should know that when the difference in electronegativity between the elements increases, the ionic character increases... by Si-S then F-Fe see this http://www.chemteam.info/Bonding/Electroneg -Bond-P...