According to the Hardy-Weinberg principle, allele and genotype freque…

The correct answer is Option (4) → The population is large and there is random mating

The Hardy-Weinberg principle says that in a population the allele frequencies stay constant from one generation to the next. This state is called genetic equilibrium. It holds only when nothing disturbs it. The book names five disturbing factors: gene migration (gene flow), genetic drift, mutation, genetic recombination and natural selection. In a large population chance changes (genetic drift) are very small, and with random mating the genotypes form in the expected proportions p², 2pq and q².

Option (1) There is mutation — Incorrect. Mutation adds new alleles, so it changes allele frequencies. It is one of the five disturbing factors.

Option (2) There is migration — Incorrect. Migration of individuals moves genes into or out of a population (gene flow). This changes gene frequencies in both the old and the new population.

Option (3) There is natural selection — Incorrect. Natural selection lets some variants survive and breed more, so their alleles become more common. It too disturbs the equilibrium.

Option (4) The population is large and there is random mating — Correct. When the population is large and mating is random, and no disturbing factor acts, the frequencies stay constant.

NCERT Extract:
Hardy-Weinberg Principle – “… This principle says that allele frequencies in a population are stable and is constant from generation to generation. The gene pool (total genes and their alleles in a population) remains a constant. This is called genetic equilibrium. … Five factors are known to affect Hardy-Weinberg equilibrium. These are gene migration or gene flow, genetic drift, mutation, genetic recombination and natural selection.”