Correct option is A
Assertion A: Atyantabhava is eternal.
This statement is true. Atyantabhava, also known as absolute non-existence, is a concept in Indian philosophy that refers to something that does not exist at any time or in any place. It is eternal because it cannot be created or destroyed.
Reason R: If a particular thing does not exist in a particular locus at any time, then it is said that there is Atyantabhava of that thing.
This statement is also true. If a particular thing does not exist in a particular locus at any time, then it means that it does not exist at all. This is the definition of Atyantabhava.
Therefore, both Assertion A and Reason R are true, and Reason R is the correct explanation of Assertion A.