(a) Both (A) and (R) are true and (R) is the correct explanation for (A).
Organic farming avoids chemical pesticides, uses natural fertilisers like cow dung, and maintains soil quality — directly making it an environment-friendly green skill essential for sustainable agriculture.
The source passage explicitly states that organic farming is "a true example of sustainable development" where farmers use natural fertilisers, avoid chemical pesticides, and maintain soil quality for future use. This directly supports both the Assertion and shows the Reason correctly explains why organic farming qualifies as a green skill — making option (a) the correct choice. Examiners expect you to pick (a) when both statements are true AND the Reason logically justifies the Assertion.