Step 1: Historical context
The Constitution of India was adopted by the Indian Constituent Assembly on 26th November 1949 but came into effect on 26th January 1950. This date was chosen to honor the declaration of independence made on 26th January 1930.
Step 2: Significance of the date
26th January was a significant date in Indian history because it marked the Purna Swaraj (complete independence) declaration by the Indian National Congress in 1930.
Step 3: Conclusion
Thus, the Constitution of India was enforced on 26th January 1950, which is celebrated as Republic Day in India.
The correct answer is option (D).