In India, National Statistics Day is observed every year on which date to honour P. C. Mahalanobis?

Introduction / Context:
National Statistics Day in India is celebrated to honour the contribution of Professor Prasanta Chandra Mahalanobis, a pioneer in statistics and economic planning. His work helped shape India's statistical system and planning processes. This day is observed every year on 29 June, his birth anniversary. For exams, this date is important because it links a key figure in Indian statistics with a nationally recognized observance.

Given Data / Assumptions:
- The observance is National Statistics Day in India.
- It is explicitly tied to honouring P. C. Mahalanobis.
- The task is to pick the correct date of the observance from among several common commemorative dates.

Concept / Approach:
The main concept is connecting Mahalanobis and statistics with the date 29 June. A useful approach is to group dates related to national intellectual figures in your memory, such as National Statistics Day on 29 June and National Science Day on 28 February. Knowing whose birth anniversary each day marks can help fix the dates firmly. Here, associating Mahalanobis, statistics and late June will guide you to the correct option.

Step-by-Step Solution:
Step 1: Note that the question specifies National Statistics Day and mentions P. C. Mahalanobis. Step 2: Recall that this day is celebrated on his birth anniversary, which falls on 29 June. Step 3: Scan the options and identify 29 June among them. Step 4: Observe that other options like 15 August and 20 October correspond to major national or international events unrelated to statistics. Step 5: Select 29 June as the correct answer, matching the known date of National Statistics Day.

Verification / Alternative check:
To verify, think about 15 August, which is India's Independence Day, and 26 January, which is Republic Day. Since these major dates already have well known meanings, they are unlikely to be reused for National Statistics Day. Similarly, 20 October and 21 September are not widely associated with statistics in the standard exam syllabus. This process of elimination supports 29 June as the correct date for the observance in honour of Mahalanobis.

Why Other Options Are Wrong:
20 October: Not officially linked with National Statistics Day and may relate to other events or none at all in the GK context.
20 July: Not recognized as National Statistics Day and may be confused with unrelated observances.
21 September: Used for different international observances such as the International Day of Peace, not for statistics in India.
15 August: Celebrated as Independence Day in India, marking freedom from colonial rule, not the achievements of Mahalanobis.

Common Pitfalls:
A common error is to confuse National Statistics Day with other national commemorative days, especially if one memorizes dates without linking them to personalities. Another pitfall is to focus only on popular dates like 15 August and assume that the answer must be one of them. To avoid such mistakes, always pair the name of the day with the individual it honours; in this case, “Mahalanobis equals statistics equals 29 June.” This conceptual pairing makes it easier to recall under exam conditions.

Final Answer:
Correct option: 29 June