Explanation:

Parliament makes laws on subjects in State List in the following scenarios -
A. When Rajya Sabha passes a resolution to that effect –
1. Parliament can make laws on a matter in state list, if the Rajya Sabha says that it is necessary in  the national interest that Parliament should make laws on that matter.
2. This resolution must be supported by two-thirds of the members of Rajya Sabha, present and  voting.
3. The resolution remains in force only for one year.
4. It can be renewed again and again but not exceeding one year at a time.
5. The laws made under the resolution too cease to have effect on the expiration of six months after  the resolution has ceased to be in force.
6. The state legislature too can make laws on the same matter, but, in case of conflict parliamentary  law prevails.
B. During a National Emergency -
1. When a proclamation of national emergency is in operation, parliament can legislate on subjects  of the state list.
2. Here too the laws become ineffective on the expiry of six months after the emergency has ceased  to operate.
3. Here again, state can make laws but in case of conflict parliamentary law prevails.
C. When States make a request for it -
1. Parliament can also make laws on subjects in the state list when the legislatures of two or more  states pass resolutions requesting the Parliament to enact laws on that matter.
2. This law enacted by the Parliament will apply only to the concerned states i.e., states who have  passed such a resolution.
3. But even other states are allowed to adopt the law by passing a resolution in their legislatures.
4. However only Parliament can amend or repeal such a law.
5. The state legislature looses the power to make a law with respect to that subject. Some examples are -Transplantation of Human Organs Act, 1994; Prize Competition Act, 1955;  Wild Life (Protection) Act, 1972; Water (Prevention and Control of Pollution) Act, 1974, etc.
D. For implementing International Agreements -

1. For implementing the international treaties, agreements or conventions, the Parliament is  authorized to make laws on any subject in the State List. Examples - Legislations related to TRIPS; Anti-Hijacking Act, 1982; etc.
E. During President’s Rule -
1. Parliament can make laws with respect to any subject in the State List in relation to that state,  when President’s rule is in force in that state.
2. Even if the President’s Rule ends, the law remains in force in the state.
3. However, State legislature can repeal or alter or re-enact that law.