Question

which one of the following scenarios would be an example of allopatric speciation?
because of a chromosomal error during egg development, a tree frog develops that has four sets of chromosomes instead of the typical two sets. this tree frog cannot mate with other typical frogs but just happened to mate with another tree frog that has four sets of chromosomes. all of their offspring have four sets of chromosomes and can only mate with other tree frogs that have four sets of chromosomes. tree frogs with four sets of chromosomes gradually become more common, and eventually, both kinds of tree frog have large geographic ranges.
members of a population of meadowlarks living in central north america became separated into two isolated populations during an ice age. after being isolated for thousands of years, the two populations met up again after glaciers retreat at the end of the ice age, but the members of the two populations can no longer interbreed.
human populations appear different from one area of the planet to another.
dogs have been selectively bred for certain traits so that different dog breeds appear different from each other.

Explanation:

Allopatric speciation occurs when a population is divided by a geographical barrier, leading to reproductive isolation and the formation of new species. The meadowlarks example shows two populations separated by an ice - age (a geographical event), becoming isolated for thousands of years, and then when they meet again, they can't interbreed. This fits the definition of allopatric speciation as the speciation is due to a geographical separation.
The dog breeding is artificial selection, the human population difference is not speciation in the biological sense (as humans are still one species), and the tree - frog example is more about a chromosomal error (sympatric speciation - related to non - geographical factors like genetic changes within the same area).

Answer:

Members of a population of meadowlarks living in central North America became separated into two isolated populations during an ice age. After being isolated for thousands of years, the two populations met up again after glaciers retreat at the end of the ice age, but the members of the two populations can no longer interbreed.