Concept:Taxonomy is the branch of Biology that deals with the classification, naming, and identification of organisms.
Explanation:Classification means grouping organisms according to shared characteristics and natural relationships.
The scientific principles behind this grouping are studied under taxonomy.
Taxonomy also includes nomenclature, which is the system of giving scientific names, but naming alone is not the whole branch.
Ecology deals with organisms and their environment, while a biological index is not a recognised branch of Biology.
Hence, the correct option is taxonomy.
Answer:C. taxonomy