By Sunil Bhardwaj

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As one of the function of the salt bridge is to help in migration of ions from one side to the other. As the transference number of cation and anion in KCl as well as \(KN{ O }_{ 3 }\) or \(N{ H }_{ 4 }N{ O }_{ 3 }\) are approximately equal i.e.$$ { t }^{ + } = { t }^{ - } = 0.5 $$ As these ions carry the current in a salt bridge between two half cells, the rate of movement of the charge in the opposite directions will be approximately same.

Secondly there will be no charge seperation across solution interface. In this way no formation of charge layers and thus liquid potential can be eliminated. Any electrolyte in which the transport number of cations and anion in same is successfully used as salt bridge. i.e. why KCl is commonly used in salt bridge.