Electron configuration:
The arrangement of electrons in an atom by a superscript, in each sublevel is known as electron configuration. For example the d block elements have (n-1)d1-10 ns1-2 electronic configuration
The atomic number if bromine is 35 thus there are 35 electrons present which fill accorindg to the Hund’s rule and aufbau principle a follows:
Br-35 1s22s22p63s23p64s23d104p5
Or [Ar] 4s23d104p5