In which orbital does an electron in a bromine atom experience the greatest effective nuclear charge?

First let us determine the electronic configuration of Bromine (Br). This is written as:

Br = [Ar] 3d10 4s2 4p5

Then we must recall that the greatest effective nuclear charge (also referred to as shielding) greatly increases as distance of the orbital to the nucleus also increases. So therefore the electron in the farthest shell will experience the greatest nuclear charge hence the answer is:

4p orbital