Because molecular bromine is a strong and toxic oxidant, excess bromine is neutralized. Addition of the aqueous sodium thiosulfate is used for that reason. Sodium thiosulfate is a good reducing agent and converts molecular bromine to sodium bromide. The thiosulfate anion is converted to sulfate anion in the process. Omitting the sodium spectator ions, write and balance the oxidation and reduction half-reactions that are occurring. (You may use H2O/H+ to attain atom balance)