Which Constitutional Amendment Act introduced changes in the Preamble to the Constitution of India by adding the words Socialist, Secular and Integrity?

Introduction / Context:
The Preamble of the Constitution of India originally declared India to be a Sovereign Democratic Republic. Later, specific words were added to reflect expanded aspirations and political commitments. This question asks which Constitutional Amendment inserted the words Socialist, Secular, and Integrity into the Preamble, an important change often discussed in exams and legal debates.

Given Data / Assumptions:

• The focus is on amendments to the Preamble, not other parts of the Constitution.
• We know that certain key words were added during the 1970s.
• Options list several amendments around that period and later.
• We assume basic familiarity with the so called mini Constitution.

Concept / Approach:
The 42nd Constitutional Amendment Act, 1976, popularly known as the mini Constitution, made extensive changes to several parts of the Constitution. Among these, it amended the Preamble to describe India as a Sovereign Socialist Secular Democratic Republic and to add the word Integrity to the phrase Unity and integrity of the Nation. This amendment is therefore directly linked to the new words named in the question.

Step-by-Step Solution:
Step 1: Recall that the Preamble was amended only once to add the words Socialist, Secular, and Integrity. Step 2: Connect this single amendment with the 42nd Constitutional Amendment Act, 1976. Step 3: Identify 42nd Amendment Act, 1976 in the list of options. Step 4: Choose this option and reject others which correspond to different constitutional changes.

Verification / Alternative check:
Constitutional references and exam guides explicitly state that the 42nd Amendment amended the Preamble. It introduced Socialist and Secular immediately after Sovereign and inserted Unity and integrity of the Nation in place of Unity of the Nation. No other amendment is associated with this set of changes. This provides strong confirmation that the 42nd Amendment Act, 1976 is correct.

Why Other Options Are Wrong:
38th Amendment Act, 1975: Primarily strengthened emergency provisions. 40th Amendment Act, 1976: Related to the Ninth Schedule and certain property matters. 44th Amendment Act, 1979: Modified emergency provisions and restored some civil liberties but did not alter the Preamble. 52nd Amendment Act, 1985: Introduced the anti defection law and added the Tenth Schedule, again without amending the Preamble.

Common Pitfalls:
Due to the large number of amendments in the 1970s, students can easily mix up amendment numbers. Some recall only that changes occurred during the emergency period and may guess the 38th or 40th Amendment. To avoid this, it is helpful to specially memorise the role of the 42nd Amendment as the mini Constitution and link it with the key additions Socialist, Secular, and Integrity in the Preamble.

Final Answer:
42nd Amendment Act, 1976