Which of the following statements about species, as defined by the biological species concept, is (are) correct?
i. biological species are defined by reproductive isolation.
ii. biological species are the model used for grouping extinct forms of life.
iii. the biological species is the largest unit of population in which successful reproduction is possible.
a) i only
b) ii only
c) i and iii
d) ii and iii
e) i, ii, and iii

C) I and III

Explanation:

The biological species concept defines species as a group of individuals that can interbreed together to give rise to fertile and viable progeny. Therefore, a biological species consists of one or more populations whose members are able to interbreed among themselves to produce fertile progeny but can not interbreed with the members of other biological species. Reproductive isolation is the criteria to classify organisms on the basis of the biological species concept.

The concept cannot be applied to the extinct organisms or the organisms that do not reproduce sexually.