An unbiased p-n junction has holes diffusing from p-region to the n-region because:

Correct option is A

In an unbiased p-n junction, holes (which are the absence of electrons) in the p-region diffuse into the n-region because the hole concentration is higher in the p-region compared to the n-region. The holes move from an area of higher concentration (the p-region) to an area of lower concentration (the n-region) due to diffusion, which is driven by the concentration gradient.