Process of formation of new species due to change in allele frequency…

The correct answer is Option (1) → Founder effect

Option (1) Founder effect — Correct. When a small group leaves a population and starts a new one, its allele frequencies can differ by chance from those of the original population. The founders carry only a small sample of the old gene pool, so the new population can drift far enough to become a different species.

Option (2) Natural selection — Incorrect. Natural selection also changes allele frequencies, but not by chance. Individuals with useful variations survive and leave more offspring, so their alleles become more common. The question describes the case named after the small group that starts the new population.

Option (3) Adaptive radiation — Incorrect. Adaptive radiation is the evolution of many different species from one ancestor, each spreading into a different habitat of one region. Darwin’s finches of the Galapagos Islands are the example. It is a pattern of many species, not a change in one small population.

Option (4) Industrial melanism — Incorrect. Industrial melanism is the rise of dark-winged moths in the polluted areas of England after industrialisation. The moths changed in colour by natural selection, but no new species was formed.

NCERT Extract:
Hardy-Weinberg Principle – “… The original drifted population becomes founders and the effect is called founder effect.”