Why is salt bridge used in a voltaic cell?
A It prevents voltage drop
B It allows flow of current by completing the circuit
C It helps in accumulation of charges
D Salt bridge form a electrolyte

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Hint: Salt bridge is used to maintain the electrical neutrality of the solution in the two half solution ,i.e oxidation half reaction and reduction half reaction.

Complete step by step answer:
A salt bridge is a U shape tube containing concentrated solution of inert electrolyte like $KCl, KNO_3$, etc. As salt bridge is made up of inert electrolyte. Inert electrolytes are those electrolytes whose ions do not take part in the redox reaction and also do not react with the electrolytes used in the oxidation and reduction half reactions of the cell. The main function of the salt bridge is to allow the movement of the ions from one solution to the other solution without mixing of the two solutions.
Therefore the main function of the salt bridge are:
1. It prevents the voltage drop.
2. It completes the electrical circuit by allowing the ions to flow from one solution to another solution.
3. Also it is a form of inert electrolyte which does not react with any of the electrolyte present in the two half cells.

Hence in the given options (A), (B) and (D) are correct.

It should be noted that salt bridges only provide a way for the transfer of ions and also to maintain the circuit electrical neutral. It does not help in accumulation of charge in the redox reaction.