Explanation

A Greenfield project refers to an entirely new facility constructed from the ground up on undeveloped land, whereas a Brownfield project involves modifying, upgrading, or expanding an existing operational facility.

* 1. Donyi Polo Airport — Correct: Located at Hollongi near Itanagar in Arunachal Pradesh, it was developed from scratch as the state’s first greenfield airport to provide all-weather commercial connectivity to the state capital.

* 2. Kushinagar International Airport — Correct: Situated in eastern Uttar Pradesh to boost the Buddhist tourism circuit, it was constructed as a newly built greenfield international airport on undeveloped land.

* 3. Vijayawada International Airport — Incorrect: Located at Gannavaram in Andhra Pradesh, it is an old operational airbase dating back to World War II. Its recent upgrades and new terminal building represent a brownfield expansion, not a greenfield project.

Therefore, only 1 and 2 have been constructed as Greenfield projects.

Hence, Option (a) is the correct answer.