Assertion: Phylogeny is the developmental history of a species.
Reason: Species is the basic unit of taxonomy.
A) Both assertion and reason are correct and the reason is the correct explanation for assertion
B) Both assertion and reason are correct but reason is not the correct explanation for assertion
C) Assertion is correct but reason is incorrect
D) Both assertion and reason are incorrect

Hint: Phylogeny is the study of evolutionary development and history of species or groups. There are seven taxonomic hierarchies representing kingdom, phylum, class, order, family, genus, and species.

Complete answer: Phylogeny is the evolutionary history of species. It gives the details of evolution. It helps in determining the ancestors of species and how species, genes evolve. Phylogeny is studied with the help of phylogenetic trees also known as a cladogram. Evolution of species is depicted by the connection of branches. Two species that have more common recent ancestors are more related than other species. Phylogenetics also plays an important role in other fields such as for conservation of endangered species, bioinformatics, and computing, depicting the source of pathogens of new diseases, DNA identification in crimes, and disputes and it helps in classifying the species according to Linnaeus classification.
Taxonomy is the arrangement of organisms on the basis of similar characteristics. It involves characterization, identification, and classification, and organisms are arranged in groups such as Kingdom, phylum, class, order, family, genus, and species. Species is the basic unit of taxonomy.
Hence, option A is correct, i.e., Both assertion and reason are correct and reason is the correct explanation for assertion.

Note: Phylogenetic study gives the details of gene, genomics and species. It gives the idea of how different species emerged from a common ancestor. Species having more recent ancestors are more related. Phylogenetic trees help in the study of the evolution of species. Taxonomy is the characterization, identification, and classification of organisms having species as the basic unit.