This involves the electromigration and migration number of ions, which is the content of electrochemistry in college physical chemistry. You can look it up. Here I tell you roughly that the migration number of ions mainly depends on the movement speed of ions in the solution, and has nothing to do with the valence and concentration of ions. When selecting salt bridge, anions and cations in electrolyte must have very close migration numbers. When a high concentration electrolyte solution is used as a salt bridge to connect the two solutions, the main diffusion comes from the salt bridge. If the anions and cations in the salt bridge have similar migration numbers, the junction potential of the solution will be minimized. However, please note that the salt bridge solution cannot react with the original solution. -The above is excerpted from the Physical Chemistry Teaching and Research Section of Tianjin University, Volume II of Physical Chemistry Higher Education Edition. If you are only a high school student, you only need to remember the commonly used salt bridges: saturated KCl aq, KNO3 aq and NH4NO3 aq. I hope I can help you ~ ~ ~