Which one of these categories has real existence?

The correct option is Species.

In biological classification, taxonomic categories represent different levels of organization. However, there is a fundamental difference in how these categories exist in nature:
1. Species: A species is the basic unit of classification. It consists of a group of individual organisms that share common characteristics, are capable of interbreeding under natural conditions, and produce fertile offspring. Because species refer to concrete, living populations of organisms that exist and interact in the physical world, they are considered to have a real, objective existence.
2. Higher Taxonomic Categories (Genus, Phylum, Kingdom): In contrast, categories like Genus, Phylum, and Kingdom are abstract, man-made taxonomic constructs. They are created by biologists to group different species based on shared evolutionary relationships and characteristics for convenience of study. These categories do not exist as concrete, interbreeding physical entities in nature.

Therefore, among the given options, only Species has a real existence in nature.