what is bond fission
 

there are two types of bond fission one is homlytic and other is hetrolytic 
homolysis -the symmetrical breaking of a covalent bond such that the both the atoms acquires one electron of the shared pair
                this fission between the same atoms 
hetrolytic - the unsymmetrical breaking of the covalent bond such that the more electronegative m acquires both the elelctron of the shared pair
                  its takes place in a  polar solvent like H₂O