Decide which of the following bonds is least polar on the basis of electronegativities of atoms,

Question

H---S, Si---Cl, N---Cl.

Answer 1

Look up the electronegativities, subtract them, and compare. The smallest difference will be the most covalent bonds (least polar).
Example:
NaCl. Na is about 0.9 and Cl is about 3.5 and the difference is about 2.6
NH3. N is about 3.0 and H is 2.1 so the different is about 0.9; thus, the N-H bond is must less polar than the NaCl bond. But we know, of course, that we call NaCl an ionic bond and NH3 bonds covalent (actually polar covalent).