Assertion (A): According to Robert May’s estimate, only about 22% of the total number of existing species have been recorded so far.

Reason (R): More than 1,00,000 plant species are yet to be discovered in India

The correct option is B Both assertion and reason are true but the reason is not the correct explanation for the assertion
India is known to cover only 2.4% of the total landmass of the world but its contribution to global species diversity is estimated to be around 8.1 %. This is the reason India is considered to be one of the 12 mega diversity countries of the world.

Based on the available inventory of described species in India, the total number of animal species in India is estimated to be around 90000 and that of plant species is around 45000.

According to the estimates of Robert May, only about 22% of the existing species of the planet have been described so far. Taking this fact into consideration, and applying the numbers to India's species inventory, we can estimate that around 1,00,000 plant species and 3,00,000 animal species are yet to be discovered in India.

Thus, both assertion and reason are true but the reason is not the correct explanation for the assertion.