The polar covalent bonds are originated when the atoms have different electronegativities but not as different as to form ionic bonds.
Here are the electronegativities of the elements involved:
element electronegativity
P 2.19
Cl 3.16
O 3.44
H 2.20
S 2.58
Of course, when the two atoms of the bond are the same, the bond is purely covalent, not polar.
So, the bondis in P-Cl, O-H, S-Cl, and H-Cl are polar covalent.
Cl - Cl bond is not polar covalent.
Answer: Cl -Cl
