Answer:
The purpose of salt bridge is
b. the salt bridge prevents the direct mixing of one half-cell solution with the other.
d.the salt bridge allows ions to migrate from one half-cell to the other.
Explanation:
Salt bridge is a structure which is placed as a bridge between two half cells of a voltaic cell. It contains a gel like agar agar and some salt like KCl.
If we do not use salt bridge, the cell will stop working after some time due to accumulation of positive ions around anode and negative ions around cathode.
So salt bridge maintains electro-neutrality (by reaction of positive ions of salt bride salt with negative ions of anodic compartment and by reaction of neagative ions of salt bride salt with positive ions of cathodic compartment).
It prevents mixing of two half cell solution but allows ions to migrate from one half-cell to the other.
