Correct Answer: option 3 i.e. salt bridge
Reason:
A voltaic cell is an electrochemical cell that employs a chemical reaction to produce electrical energy. In voltaic cell, they half-cell (i.e anodic and cathodic compartment) are connect salt bridge. Salt facilitates motion of ions, due to which electricity flows. In absence of salt bridge, the electricity will not flow, because circuit is not complete.