Option 1 states that both Assertion (A) and Reason (R) are true, and R is the correct explanation of A. This means that Nalanda being the center of Buddhist learning in the post-Gupta period is true, and it was patronized by the Pala rulers, which is the correct explanation for why Nalanda became a center of Buddhist learning. However, this option is incorrect because R is not a correct explanation of A. Although Nalanda was indeed patronized by the Pala rulers, this alone does not explain why Nalanda became a center of Buddhist learning.

Option 2 is the correct answer. It states that both Assertion (A) and Reason (R) are true, but R is not a correct explanation of A. This means that Nalanda was the center of Buddhist learning in the post-Gupta period, and it was indeed patronized by the Pala rulers. However, the reason for Nalanda becoming a center of Buddhist learning cannot solely be attributed to the patronage of the Pala rulers.

Option 3 states that Assertion (A) is true, but Reason (R) is false. This is not correct because both A and R are true.

Option 4 states that Assertion (