Question

mention two main circumstances in which the parliament can legislate on state subject

Answer 1

Two main circumstances in which the parliament can legislate on state subject are:-
1.During the proclamation of a national emergency (Article 250).
2.When a resolution is passed by the Rajya Sabha by 2/3 majority,it makes it lawful for the Parliament to legislate on a subject mentioned in the State List in national interest (Art.249).
Hope it helps!

Answer 2

During the proclamation of emergency and when the rajya sabha declares that a state list subject has assumed national importance.