In figure ${\mathrm{V}}_0$ is the potential barrier across a p-n junction, when no battery is connected across the junction, then 
 

• P-N junctions are forward biassed when they oppose a potential barrier and reverse biassed when they favour a potential barrier. increasing the potential barrier as a result. 1 is reversely biassed, while 3 is forwardly biassed.
• The junction's forward bias is represented by 3 and its reverse bias by 1, respectively.

Hence the correct answer is 3 correspond to forward bias of junction and 1 corresponds to reverse bias of junction .