Assertion(a): “Biological species” concept helps to ask how species are formed

Reason(r): Concept of biological species is centred around the question of how reproductive isolation comes about

The correct option is: (a) is true, (r) is incorrect.

Explanation of Assertion (a):
The biological species concept, primarily formulated by Ernst Mayr, defines a species as a group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups. By focusing on the ability of individuals to interbreed and produce fertile offspring, this concept directs attention to the mechanisms that keep populations distinct. Consequently, it provides a theoretical framework to ask how new species arise (speciation) by looking at how barriers to gene flow are established. Therefore, Assertion (a) is true.

Explanation of Reason (r):
The biological species concept defines species based on the existence of reproductive isolation, but the concept itself is not centered around the genetic or evolutionary question of how reproductive isolation comes about. Rather, reproductive isolation is used as the defining criterion to identify species boundaries. The mechanisms and processes of how isolation arises belong to the study of speciation mechanisms rather than the definition of the species concept itself. Therefore, the statement in Reason (r) is considered incorrect in this context.