Dear student kindly post your the questions one by one--
 Liquid junction potential or diffusion potential is the potential which develops when two solutions of different concentrations are in contact with each other,then more concentrated solution will have a tendency to diffuse into the less concentrated one.The rate of diffusion of each ion will be roughly proportional to its speed in an electric field.If the anions diffuse more rapidly than the cations,they will diffuse ahead into the dilute solution,leaving the latter negatively charged and the concentrated solution positively charged which will result in an electrical double layer of positive and negative charges at the junction of the two solutions.Thus at the point of junction,a potential difference will develop because of the ionic transfer.This potential is called liquid junction potential whose magnitude depends on the relative speeds of the ions' movement.
 Salt bridge minimizes this diffusion potential,that develops when any two phases (like the two solutions) are in contact.This potential adds to the cell voltage and introduces a degree of uncertainity of cell voltage measurements.With the salt bridge, we create two liquid junction potentials,but they tend to cancel each other out.