In an unbiased p-n junction, holes diffuse to region from – region because
(a) free electrons in the -region attract them.
(b) they move across the junction by the potential difference.
(c) hole concentration in p-region is more as compared to n-region.
(d) All of the above.

(c) is the correct option.

The charge carriers’ natural tendency is to disperse from the greater concentration zone to the lower concentration region. As a result, holes disperse from the p-region to the n-region in an unbiased p-n junction because the p-region has a higher concentration of holes than the n-region.