Step 1: Understand Delhi's special status.
As the national capital, Delhi cannot be a normal state, yet it needs an elected body, so a special framework was created.
Step 2: Identify the amendment.
The 69th Constitutional Amendment Act, 1991 created this arrangement.
Step 3: Know what it added.
It inserted Articles 239AA and 239AB, renamed the Union Territory as the National Capital Territory of Delhi, and gave it a Legislative Assembly and Council of Ministers.
Step 4: Rule out the others.
The 72nd dealt with Tripura tribes, the 73rd with Panchayati Raj, and the 76th with Tamil Nadu reservation.
Answer: 69th Constitutional Amendment Act (Option 3).