The correct answer is option 3, 26 November, 1949. The Constitution of India was adopted on this date. Option 1, 26 January, 1950, is incorrect as this is the date when the Constitution came into effect. Option 2, 26 January, 1949, is incorrect as it does not correspond with the date of adoption. Option 4, 31 December, 1949, is also incorrect as the Constitution was adopted before this date. It is important to note that the adoption of the Constitution refers to the formal approval and acceptance of the document, while the date of coming into effect signifies when the provisions and laws of the Constitution officially start being implemented.