GST on retained SKO applies to the net quantity used for n paraffin extraction, not on SKO returned to refinery. GST applies to the net quantity of superior kerosene oil (SKO) retained by LAB manufacturers for extraction of n paraffin used in manufacturing Linear Alkyl Benzene; the refinery is liable to pay GST only on that retained quantity, while returned SKO does not attract GST unless the refinery supplies it to another person.