The basic structure theory of the Constitution of India implies that

The Basic Structure doctrine holds that certain fundamental features of the Constitution are inviolable and cannot be abrogated by parliamentary amendment; it introduces a substantive limitation beyond the procedural mode in Article 368, preventing Parliament from rewriting core constitutional principles [1]. The Supreme Court in Kesavananda Bharati emphasized that the basic elements reflected in the Preamble form part of this protected core and cannot be altered by amendment [3]. Option (1) thus captures the doctrine’s essence. Option (2) is too absolute: fundamental rights may be amended so long as the amendment does not destroy the Constitution’s basic structure [2]. Option (3) is a correct procedural statement but does not express the doctrine’s substantive limit; option (4) incorrectly frames the Preamble as not part of the Constitution while also mischaracterising the doctrine [3].

Sources

1. [1] Introduction to the Constitution of India, D. D. Basu (26th ed.). > Chapter 10: Procedure for Amendment > p. 197
2. [3] Indian Polity, M. Laxmikanth(7th ed.) > Chapter 5: Preamble of the Constitution > 1 AMENDABILITY OF l THE PREAMBLE > p. 48
3. [2] Introduction to the Constitution of India, D. D. Basu (26th ed.). > Chapter 8: FUNDAMENTAL RIGHTS AND FUNDAMENTAL DUTIES > CHAP. 8 Fundamental Rights and Fundamental Duties 97 > p. 97