Under which Constitutional Amendment Act was Sikkim formally admitted into the Union of India as a full State of the Indian Union?

Introduction / Context:
Sikkim's integration into India is an important topic in modern Indian political history and constitutional development. Initially associated with India as a protectorate, Sikkim later became an associate State and finally a full State of the Indian Union. This transition was implemented through specific Constitutional Amendment Acts. Examinations often test the precise amendment number that granted Sikkim full statehood and admitted it into the Union of India as a State.

Given Data / Assumptions:
- The question asks about the Constitutional Amendment Act that admitted Sikkim into the Union of India as a full State.
- The options are the 35th, 36th, 37th and 38th Constitutional Amendment Acts.
- It is assumed that the student is familiar with the broad sequence of events relating to Sikkim's political integration with India.
- The distinction between an associate State status and full statehood is important in answering this question correctly.

Concept / Approach:
Sikkim's integration involved more than one constitutional step. The 35th Constitutional Amendment Act provided for Sikkim's status as an associate State and inserted Article 2A and the Tenth Schedule as it then existed for this purpose. However, Sikkim was later made a full State of the Indian Union through the 36th Constitutional Amendment Act, which removed the earlier associate State provisions and inserted special provisions for Sikkim in Article 371F and included it in the First Schedule as a State. The correct approach is therefore to recall which amendment actually converted Sikkim into a State and admitted it into the Union, not merely associated it.

Step-by-Step Solution:
Step 1: Recall that the 35th Constitutional Amendment Act granted Sikkim an associate State status, introducing Article 2A and a special schedule. Step 2: Remember that this arrangement was temporary and was superseded when Sikkim opted for full integration with India. Step 3: The 36th Constitutional Amendment Act, 1975, provided for Sikkim to be admitted into the Union of India as a full State and inserted Article 371F with special provisions relating to Sikkim. Step 4: Compare this with the other amendments listed: the 37th and 38th Amendment Acts dealt with different constitutional matters and not specifically with Sikkim's statehood. Step 5: Therefore, the amendment that admitted Sikkim into the Union of India as a full State is the 36th Constitutional Amendment Act.

Verification / Alternative check:
Standard polity textbooks and documents on constitutional amendments clearly state that the 36th Constitutional Amendment Act is the one through which Sikkim became the twenty second State of India in 1975. They often explain the sequence: associate State status under the 35th Amendment followed by full statehood under the 36th Amendment. No credible source attributes Sikkim's admission as a State to the 37th or 38th Amendments, which are concerned with other issues. This consistency across authoritative references confirms the choice of the 36th Constitutional Amendment Act as correct.

Why Other Options Are Wrong:
Option A (35th Constitutional Amendment Act) is wrong in the context of this question because it dealt with Sikkim's associate State status, not its final admission as a full State into the Union of India.
Option C (37th Constitutional Amendment Act) is wrong because this amendment relates to different constitutional provisions and does not concern Sikkim's statehood.
Option D (38th Constitutional Amendment Act) is wrong because it primarily dealt with issues such as emergency provisions and did not make Sikkim a State of the Union.

Common Pitfalls:
A common confusion arises between the 35th and 36th Amendment Acts because both are associated with Sikkim and occurred in close succession. Students sometimes remember that Sikkim is linked with the 35th Amendment and forget the separate step by which it became a full State. Another pitfall is to treat amendment numbers in this range as interchangeable without linking them to their specific subject matter. To avoid such errors, it is useful to associate 35th with associate State status and 36th with full statehood and admission into the Union.

Final Answer:
Sikkim was formally admitted into the Union of India as a full State through the 36th Constitutional Amendment Act.