The rate of genetic drift would be greatest in b) a small population that is geographically isolated from its parent population.
Genetic drift refers to the changes in allele frequencies in a population due to random sampling of organisms. In smaller populations, the effects of random fluctuations in allele frequencies are more pronounced because each individual’s genetic contribution has a larger impact on the overall gene pool. When a population is geographically isolated, it is cut off from gene flow with other populations, thus preventing the mix of genes that could help stabilize the allele frequencies. As a result, in a small, isolated population, genetic drift can lead to significant changes in the genetic makeup over generations, increasing the likelihood of fixation or loss of alleles.