The potentials are applied to the four p-n junctions as shown below:…

The correct answer is Option (3) → (B), (C) and (D) only

A p-n junction is forward biased when the \textbf{p-side (anode)} is at a higher potential than the \textbf{n-side (cathode)}.

We check $V_p > V_n$ in each case:

(A)

$V_p = -5V, \quad V_n = -3V$

$-5 < -3$

p-side is at lower potential $\rightarrow$ Reverse biased

(B)

$ V_p = 0V, \quad V_n = -3V$

$0 > -3$

p-side higher $\rightarrow$ Forward biased

(C)

$V_p = 7V, \quad V_n = 3V$

$7 > 3 $

p-side higher $\rightarrow$ Forward biased

(D)

$ V_p = -10V, \quad V_n = -20V $

$ -10 > -20 $

p-side higher $\rightarrow$ Forward biased