Context: The Dhaula Kuan Metro Station is located on the Delhi Airport Express Line of the Delhi Metro. This station is the only elevated one along the Airport Express Line and features check-in facilities. It did not commence operations along with the rest of the line and trains ran through the station without stopping initially. It was opened to the public for the first time on Independence Day, 15 August 2011.

Question: on which line is dhaula kuan metro station?
Steam of consciousness below:

The relevant information to answer the above question is: The Dhaula Kuan Metro Station is located on the Delhi Airport Express Line of the Delhi Metro.
So, the answer is the Delhi Airport Express Line of the Delhi Metro.