The isotopes of a element is defined as the atoms having same atomic number and different mass number.
As per periodic table Br has atomic umber Z=35 and its atomic mass is given as 79.904 or 79.
As per the question nothing has been mentioned .
so all the atoms whose atomic number will correspond to 35 will be considered as the isotope of bromine.
Generally Bromine exhibits two isotopes which are stable.The isotopes are Bromine-81 and Bromine-77.
Some times during the process of gamma decay Bromine forms many radio isotopes also which are unstable.
