The correct option is (a).
Explanation
In biology, the most widely accepted definition of a species is based on the Biological Species Concept proposed by Ernst Mayr. It defines a species as a group of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups.
Statement 1 is Correct:
Members of the same species share a common gene pool and exhibit fundamental similarities in their morphological (physical), anatomical, and physiological characteristics. While variations exist, the core characteristics remain common across the group.
Statement 2 is Incorrect:
A defining characteristic of a species is the ability of its members to interbreed among themselves to produce fertile offspring. Members of a species generally cannot reproduce fertile offspring with members of other species. If interspecific breeding occurs (e.g., between a horse and a donkey), the offspring (mule) is typically sterile.
Statement 3 is Incorrect:
A species consists of populations that are capable of interbreeding with one another. The statement incorrectly suggests that these populations are "incapable" of interbreeding. Gene flow between populations of the same species is essential to maintain the species' integrity.
Key Takeaway:
A species is defined by reproductive isolation; members can breed with each other to produce fertile offspring but are reproductively isolated from members of other species.