Does not participate chemically in the cell reaction.
Stops the diffusion of ions from one electrode to another.
Is necessary for the occurrence of the cell reaction.
Ensures mixing of the two electrolytic solutions.
Solution
Salt bridge is introduced to keep the solutions of two electrodes separate, such that the ions in electrode donot mix freely with each other. But it cannot stop the process of diffusion.It does not participate in the chemical reaction. However, it is not necessary for occurence of cell reaction, aswe know that designs like lead accumulator, there was no salt bridge, but still reactions takes place.