(1) No tax shall be payable under this Act on sales or purchases of goods which have taken place--
         (a) in the course of inter-State trade or commerce;
         (b) outside the State of Bihar;
         (c) in the course of import of goods into, or, export of goods out of, the territory of India.
     (2) The provisions of the Central Sales Tax Act, 1956 (74 of 1956) shall apply for determining when a sale or purchase of goods shall be deemed to have taken place in any of the ways mentioned in clause (a) or clause (b) or clause (c) of sub-section (1).