(A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A).
Catenation is the ability of carbon to bond with other carbon atoms, forming long chains, branched chains, and ring structures.
Source: Chapter 4, Section 4.2 Versatile Nature of Carbon
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The assertion directly describes the structural outcomes (chains, branches, rings) of catenation, and the reason correctly names and defines that property. Since R directly explains why A is true, option (A) is correct. Remember: catenation → chains/branches/rings is a direct cause-effect link, so R is the correct explanation, not just a related true fact.