While the flushing for the chilled water system.. we start with static flushing, then dynamic flushing then finally chemical fluching and after completing the flushing we add the pasivation chemicals.. my question is what type of chemicals to be used while flushing and what is the purpose of using.. and what is the type of pasivations to be added as final chemical.. and what is its funcation

You done your job, meanwhile refer to water specialist in order to give you the proper chemicals for passivation and the final chemical to inject to your system. Remember just adding chemical without the proper recommendation by the specialist can deteriorate your entire system.