(a) A salt bridge completes the circuit by allowing the migration of anions from one container into the salt bridge and from the salt bridge into the other container.
(b) The salt bridge prevents the physical transference/diffusion of the electrolytes from one container to the other.
(c) A salt bridge helps in maintaining the charge balance in the reactions taking place at the two containers by releasing counter ions into the solution.
(d) A salt bridge eliminates a direct contact between the two solutions, and thus minimizes the liquid junction potential. Due to the unequal rates of migration of the cations and anions across a liquid-liquid junction give rise to a potential difference across the junction.