GST exempt supplies: reverse charge and Schedule III rules affect input tax credit availability for suppliers. Section 17(3) treats reverse charge supplies, transactions in securities, and sale of land and certain buildings as exempt supplies for ITC reversal purposes, applying the classification to the outward supplier. The Explanation allows full input tax credit for activities listed in Schedule III (which are 'not supplies'), subject to exclusions for sale of land, completed buildings and warehoused goods before home-consumption clearance.