Explanation:

• The Constitution of India has vested the ‘residuary powers’ with the Centre. Residuary powers are those powers which can be made by the parliament only. It is different from 3 lists, union list, state list, and concurrent list. But, the final authority to decide whether a matter falls under the list of residuary powers or not, rests with the Supreme Court. 
• The concept of Residuary powers of the Centre was borrowed from Canada.
• Therefore Both A and R are true but R is not a correct explanation of A. Hence option 2nd is correct.