The bromine atom possesses 35 electrons. It contains 6 electrons in 2p orbital, 6 electrons...

The nuclear charge that an electron (part of a multi-electron atom) experiences depends on the separation of the orbital in which the electron is located from the nucleus. As the distance increases, the effective nuclear charge will decreases. Among p-orbitals, 4p orbitals are farthest from the nucleus of bromine atom with (+35) charge. Hence, the electrons in the 4p orbital will experience the lowest effective nuclear charge. These electrons are shielded by electrons present in the 2p and 3p orbitals along with the s-orbitals. Therefore, they will experience the lowest nuclear charge.