The question involves evaluating both the Assertion (A) and the Reason (R) and choosing the most appropriate answer from the options provided. Let's analyze them:
Assertion (A): Four distinctive characteristics of phylum Chordata are notochord; single, dorsal, tubular nerve cord; pharyngeal pouches and postanal tail.
Reason (R): The distinctive characteristics of phylum Chordata remain unchanged throughout the life of these animals.
Analyzing Assertion (A): This is a true statement. The four characteristics mentioned are indeed the distinctive features of phylum Chordata.
Analyzing Reason (R): This statement is incorrect. The distinctive characteristics mentioned might not always remain unchanged throughout the life of these animals. For example, in some chordates, the notochord is replaced by a vertebral column during development (such as in vertebrates).
Given this evaluation:
Therefore, the correct answer is:
Option 3: (A) is correct but (R) is not correct.
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