Explanation:

Understanding the timeline of the Indian Constitution's creation is crucial. - **Option A (October 26, 1949):** This date is incorrect. While the Constituent Assembly was actively drafting and debating the Constitution around this period, the final adoption did not occur on this specific day. - **Option B (November 26, 1949):** This is the correct answer. On November $26$, $1949$, the Constituent Assembly of India formally adopted, enacted, and gave to themselves the Constitution of India. This day is celebrated as 'Constitution Day' (Samvidhan Diwas). While some provisions related to citizenship, elections, provisional Parliament, etc., came into force immediately, the major part of the Constitution came into effect later. - **Option C (December 26, 1949):** This date is incorrect. No significant event related to the adoption or commencement of the Constitution took place on this day. - **Option D (January 26, 1950):** This date marks the 'commencement' of the Constitution, when India officially became a Republic. On this day, the remaining and major parts of the Constitution came into full effect. However, the question specifically asks for the date of 'adoption and passing' by the Constituent Assembly, which precedes the commencement date.