When did the provisions of this Constitution relating to reservation for Scheduled Castes and Scheduled Tribes come into effect?
The provisions of this Constitution relating to reservation for Scheduled Castes and Scheduled Tribes came into effect when the Constitution was first enacted. The specific period mentioned (80 years in respect of clause (a)) indicates that this provision is expected to be valid until a certain date in the future, 80 years after the commencement of the Constitution. However, the context does not specify an exact commencement date for the Constitution, so it's not possible to provide a specific year or date when the provisions came into effect based on the information provided here.