Detailed Solution:
The correct answer is “(A) is false, but (R) is true”.
The Assertion (A) is partly true but not entirely accurate. The Supreme Court does have a significant role in determining the constitutional validity of laws (including both central and state laws). However, the jurisdiction over the constitutional validity of Central laws is not exclusive to the Supreme Court.
High Courts also have the authority to review the constitutionality of laws within their jurisdiction.
The Reason (R) is true. The Supreme Court is often referred to as the guardian of the Constitution, as it is responsible for interpreting the Constitution, ensuring that laws and government actions are consistent with it, and protecting fundamental rights.