Answer:
4.HBr
Step-by-step explanation:
Polar bonds are formed when the elements of the molecule have different electronegativities, and they are not canceled by the arrangement of the molecule.
In this case, the four molecules have elements with different electronegativities.
In the H2Se molecule and in the SiH4 molecule, the differences of electronegativities are canceled as we can see in the following graph:
For the other two molecules, HBr will have the most polar bond because the difference of electronegativity between H and Br is higher than the difference of electronegativity between H and P.