The Constitution of India was adopted on 26 November 1949 and came into force on 26 January 1950, celebrated as Republic Day.
Step 1: Analyze the options.
- (A) Independence Day.
- (B) Correct.
- (C) Adoption date.
- (D) Gandhi Jayanti.
Step 2: Conclusion.
Hence, the correct answer is (B).
Final Answer:
\[
\boxed{(B) \, 1950}
\]