In the depletion region of a diode:

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

1. (a, b)

2. (a, b, d)

3. (c, d)

4. All options are correct

(4) Hint: Depletion zone is formed due to diffusion of e from n to p side.
The space-charge regions on both the sides of the p-n junction which has immobile ions and entirely lacking of any charge carriers will form a region called the depletion region of a diode. The number of ionized acceptors on the p-side equals the number of ionized donors on the n-side.