The correct answer is option 2: Parliament alone. In the Indian federal system, legislative powers are divided between the central government (Parliament) and the state governments. The Constitution of India provides three lists - Central List, State List, and Concurrent List - that enumerate the subjects on which each level of government can legislate. However, if a subject is not mentioned in any of these lists, it falls into the category of "residual matters." In such cases, only Parliament has the authority to legislate. This means that Parliament alone can make laws on matters that are not explicitly mentioned in the Central, State, or Concurrent Lists. Therefore, option 2 is the correct answer.