Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): Petromyzon dies within a few days after spawning in fresh water. Reason (R): Petromyzon is a marine organism that migrates to fresh water for spawning. In the light of the above statements, choose the correct answer from the options given below:

Step-by-step solution

Assertion (A) is correct because Petromyzon (a cyclostome) migrates to fresh water to spawn and dies within a few days after the process. Reason (R) is also correct because cyclostomes are marine organisms that exhibit anadromous migration (migrating from marine to fresh water for spawning). However, Reason (R) is not the correct explanation for Assertion (A). The migration to fresh water is a prerequisite for spawning, but the actual cause of death is the physiological exhaustion and changes following the spawning