The correct answer is: Both Assertion (A) and reason (R) are correct  but R is not the correct explanation of A.

Explanation:

• The assertion that the use of fertilizers greatly enhances crop productivity is generally true. Fertilizers provide essential nutrients to plants, which can significantly improve crop growth and yield.
• However, the reason that irrigation is very important in increasing crop productivity is also true, but it's not the correct explanation for the assertion about the use of fertilizers. While irrigation is indeed crucial for crop growth, it primarily ensures the availability of water to crops, whereas fertilizers supplement essential nutrients. Both irrigation and fertilizers contribute independently to enhancing crop productivity, but one is not the direct explanation for the other.