(a) there are no mobile charges

(b) equal number of holes and electrons exist, making the region neutral

(c) recombination of holes and electrons has taken place

(d) immobile charged ions exist

Answer:

All of the above options: (a), (b), (c) and (d) are correct.

Explanation:

The depletion region of a p-n junction is the area where no mobile charge carriers, like electrons and holes, are present, and it acts as a barrier, preventing electrons from flowing from the n-side and holes from flowing from the p-side. Diffusion of charges happens as a result of the presence of a concentration gradient, which leads to the establishment of depletion areas. However, as diffusion is taking place, holes and electrons are recombining. As a result, a depletion area is generated, which is completely devoid of mobile charge carriers. As a result, we can say that

(1) There are no mobile charge carriers in the depletion region.

(2) The region is neutral because it contains an equal number of holes and electrons.

(3) The region’s formation is caused by recombination that has already occurred.

(4) Now we have the immobile charges that have been recombined.

As a result, all four choices A, B, C, and D are correct.