The correct answer is option 4, Padmaja Naidu Himalayan Zoological Park. This zoo is located in Darjeeling, India and is considered the highest altitude zoo in the world. It is situated at an elevation of approximately 7,000 feet (2,134 meters) above sea level.

Option 1, Cheyenne Mountain Zoo, is located in Colorado Springs, United States. While it is a popular zoo, it is not the highest altitude zoo in the world.

Option 2, Pandit G. B. Pant High Altitude Zoo, is located in Nainital, India. Although it has "high altitude" in its name, it is not the highest altitude zoo in the world.

Option 3, Himalayan Zoological Park, Gangtok, is also located in India. While it is located in the Himalayan region, it is not considered the highest altitude zoo in the world.

Therefore, option 4, Padmaja Naidu Himalayan Zoological Park, is the correct answer as it is situated at the highest altitude among the given options.