You’ve likely heard of polar bears (Ursus maritimus) and grizzly bears (Ursus arctos horribilis). Have you heard of a grolar bear or a pizzly bear? These might be unfamiliar because they are the offspring of matings between polar bears and grizzlies. A handful of these animals have been born in zoos; three have been documented in nature. Due to their rarity, only a few grolars (grizzly dad and polar bear mom) or pizzlys (polar bear dad and grizzly mom) have been studied in detail. Their fur color, head shape and ear shape (see figures below) are striking intermediates between the phenotypes of their parents.The origin of polar bears was the result of:
a. peripatric speciation.
b. sympatric speciation.
c. allopatric speciation.

When the population belonging to the same biological species becomes separated from each other due to some geographical factor such that no gene flow can occur between the two separated populations then the speciation that occurs on account of this is known as allopatric speciation.
The geographical isolation that separates the two groups can be the origin of a mountain, the formation of islands, volcanic eruption, etc. which prevents the two groups fro mating with each other and ultimately causes their lineage to speciate.
Although the two separate populations are unable to mate due to geographical factors, if the two populations are allowed to mate again, given that they have not been separated very long ago, they can give rise to hybrids.
Thus, in the given question it is given that polar bears and grizzly bears have been mated and hybrids have been produced and this points out to the fact that polar bears are result of allopatric speciation.