In a suit against the Central Government the authority to be named as defendant  is: 

Art. 300. Suits and proceedings The Government of India may sue or be sued by the name of the Union and the Government of a State may sue or be sued by the name of the State and may, subject to any provisions which may be made by Act of Parliament or of the Legislature of such State enacted by virtue of powers conferred by this Constitution, sue or be sued in relation to their respective affairs in the like cases as the Dominion of India and the corresponding Provinces or the corresponding Indian States might have sued or been sued if this Constitution had not been enacted.