Question

under what circumstances can president's rule be imposed in a state???

Answer 1

During an emergency the president's rule can be opposed in a state

Answer 2

When the  president gets involved in massive and evident corruption and criminal activities the parliament may propose a bill for the members of parliament to make a decision of impeachment if more than two thirds support the bill then the president may be imposed and the deputy president may take over the remaining term as the weight for the next general elections.