In calendar calculations for Indian history, 26 January 1950, the date on which the Constitution of India came into effect, fell on which day of the week?

Introduction / Context:
This problem combines historical knowledge with calendar reasoning. The date 26 January 1950 is important because the Constitution of India came into effect on that day, making it the first Republic Day. Many competitive exams expect you to know, or to be able to calculate, the day of the week for such landmark dates.

Given Data / Assumptions:
- Date of interest: 26 January 1950.
- Calendar: Gregorian calendar.
- We must determine the weekday on this date.
- No additional reference date is provided, so you can either recall this as a standard fact or compute it from a known anchor date using day counting methods.

Concept / Approach:
You can approach this in two ways:
1. Treat it as a memorised historical fact: 26 January 1950 was a Thursday.
2. Use a calendar algorithm like the odd days method or Zellers congruence, starting from a known reference date and working through the years, counting leap years and ordinary years correctly, then moving through the months and days in 1950 up to 26 January.
In either case, careful accounting of leap years is essential for accuracy.

Step-by-Step Solution:
Step 1: Recognise that 1950 is not a leap year because it is not divisible by 4.Step 2: Choose a convenient reference date whose weekday you know, such as 1 January 1900 or 1 January 2000, and compute the total number of days between that reference and 26 January 1950.Step 3: Break the count into complete years and partial years, identifying leap years among the complete years and adding 366 days for each leap year and 365 days for each ordinary year.Step 4: Convert the total number of days into odd days by taking the total modulo 7.Step 5: Starting from the weekday of the reference date, move forward by the number of odd days to determine the weekday of 1 January 1950, then move forward through the days in January to reach 26 January.Step 6: This careful calculation leads to Thursday as the weekday for 26 January 1950.

Verification / Alternative check:
Because this is a nationally significant date, many reliable sources explicitly mention that the first Republic Day, 26 January 1950, was observed on a Thursday. Cross checking with printed calendars or trusted commemorative records confirms that your calculation and the memorised fact agree on Thursday.

Why Other Options Are Wrong:
Monday, Tuesday, Wednesday and Friday are all weekdays that are off by one or more days from the correct weekday. If you miscount leap years, start from an incorrect anchor date, or make an arithmetic error when finding odd days, you can easily land on one of these distractor options. However, none of them matches the historically recorded weekday for this date.

Common Pitfalls:
Typical mistakes include assuming every year divisible by 4 is a leap year without considering century rules, or forgetting that February of a given year might change the number of days when counting into that year. For this specific date early in the year, a small error in the year counting can shift the weekday results significantly. Always divide the problem into clearly defined year and month segments and double check each sum.

Final Answer:
26 January 1950 fell on a Thursday.