In this error-spotting sentence, identify the part which contains a grammatical mistake in the description of Republic Day and the Purna Swaraj declaration.

Introduction / Context:
Error spotting questions help develop an eye for precise and grammatically correct English. This sentence refers to the historical reason why the 26th of January was chosen in India, linking it with the Purna Swaraj declaration of 1930. The task is to identify which numbered part of the sentence contains a mistake in expression or structure, without altering the factual meaning.

Given Data / Assumptions:

• Part 1: The 26th of January was chosen
• Part 2: to commemorate the Purna Swaraj
• Part 3: declaration for the complete independence, of 1930.
• Part 4: No error
• We assume the reference is to the historic declaration of complete independence made in 1930.

Concept / Approach:
The structure should connect the noun declaration with a proper preposition and avoid unnecessary punctuation. In standard English, we say declaration of complete independence rather than declaration for the complete independence. The comma before of 1930 is also not required and disrupts the flow of the phrase. Therefore, the main grammatical issue lies in part 3, where both the preposition and the comma use are incorrect.

Step-by-Step Solution:
Step 1: Read the sentence as a whole to understand the intended meaning. Step 2: Check part 1, which correctly states The 26th of January was chosen. Step 3: Check part 2, which correctly uses to commemorate followed by the proper noun the Purna Swaraj. Step 4: Examine part 3, which reads declaration for the complete independence, of 1930. Step 5: Notice that declaration takes the preposition of, not for, and that the comma before of 1930 is unnecessary, marking part 3 as erroneous.

Verification / Alternative check:
Consider the corrected phrasing: to commemorate the Purna Swaraj declaration of complete independence of 1930. This version reads smoothly and matches standard historical writing. Parts 1 and 2 remain unchanged in this corrected sentence, confirming that they were already correct. The only changes occur within the words and punctuation of part 3, which confirms that the error lies there. Therefore, the correct answer is the part labelled 3.

Why Other Options Are Wrong:
Part 1 correctly uses the definite article and ordinal number in The 26th of January was chosen, which is standard phrasing.

Part 2 uses the infinitive to commemorate properly, followed by the name of the resolution, and there is no grammatical fault.

Part 4 represents the No error choice and is incorrect because we have already identified problems in part 3.

Common Pitfalls:
A common trap in such questions is to focus only on subject verb agreement and ignore the accuracy of prepositions and punctuation. Learners might also be distracted by the historic content and overlook the small but important difference between declaration for and declaration of. Paying attention to collocations, that is, which words naturally go together, is key for success in this type of question.

Final Answer:
The error is in part 3 of the sentence.