Which Article of the Constitution provides that it shall be the endeavour of every State to provide adequate facility for instruction in the mother tongue at the primary stage of eduction ?

Article 350A of the Constitution specifically deals with provision for instruction in the mother tongue at the primary stage; it makes it the endeavour of every State to provide adequate facilities for such instruction, and the Supreme Court has construed the article in cases concerning the medium of instruction for linguistic minorities [1]. Relatedly, measures for protection of linguistic minorities include provisions such as the creation of a Special Officer for Linguistic Minorities (Article 350-B) inserted by the Seventh Constitutional Amendment, whose duty is to investigate safeguards provided to linguistic minorities under the Constitution [2]. Together these provisions form part of the constitutional scheme protecting cultural and educational rights of linguistic minorities.

Sources

1. [1] Introduction to the Constitution of India, D. D. Basu (26th ed.). > Chapter 33: LANGUAGES > Violation of Articles 27, 351. > p. 473
2. [2] Laxmikanth, M. Indian Polity. 7th ed., McGraw Hill. > Chapter 75: Rights and Liabilities of the Government > CONSTITUTIONAL PROVISIONS > p. 551