In figure given below V0 is the potential barrier across a p-n junction, when no battery is connected across the junction.
                      
 
1. 1 and 3 both correspond to forward bias of junction.
2. 3 corresponds to forward bias of junction and 1 corresponds to reverse bias of junction.
3. 1 corresponds to forward bias and 3 corresponds to reverse bias of junction.
4. 3 and 1 both correspond to reverse bias of junction.
(2) Hint: The potential barrier depends on the biasing of the junction.
When a p-n junction is forward biased, it opposes the potential barrier junction, when the p-n junction is reverse biased, it supports the potential barrier junction, resulting in an increase in potential barrier across the junction.