To decide which of the following bonds is least polar based on the electronegativities of the atoms (H---S, Si---Cl, N---Cl), we need to compare the electronegativity values of the atoms involved in each bond.
Electronegativity is a measure of an atom's ability to attract electrons towards itself in a chemical bond. It is usually represented by the Pauling scale, which assigns numerical values to different elements. The higher the electronegativity value, the greater the atom's ability to attract electrons.
Now, let's look at the electronegativity values of the atoms involved in each bond:
H (hydrogen) - electronegativity value of 2.20
S (sulfur) - electronegativity value of 2.58
Si (silicon) - electronegativity value of 1.90
Cl (chlorine) - electronegativity value of 3.16
N (nitrogen) - electronegativity value of 3.04
Cl (chlorine) - electronegativity value of 3.16
In general, when the electronegativity difference between two atoms is larger, the bond is more polar. The bond with the least electronegativity difference would be the least polar bond.
Comparing the electronegativity differences for each bond:
H---S: |2.20 - 2.58| = 0.38
Si---Cl: |1.90 - 3.16| = 1.26
N---Cl: |3.04 - 3.16| = 0.12
Based on the calculations, the bond with the least electronegativity difference, and therefore the least polar bond, is N---Cl.
To summarize, the bond N---Cl is the least polar bond among the given options based on the electronegativities of the atoms involved.