Question:

In the following figure, the diodes which are forward biased, are (a), (b) and (d); (c) and (a); (b) and (d); (c) only; (c) and (a); (a), (b) and (d)

(b) and (d)

(a), (b) and (d)

Only in (a) and (c), diodes are forward biased. As, p-type should be higher potential and n-type at lower potential.