1. Which is Longest road tunnel in the World ?

Answer: Lærdal Tunnel (Norway - 24.51 kilometre)

2. Which is Largest library in the world ?

Answer: United State Library of Congress, Washington D.C.

3. Which is highest dam in world ?

Answer:

Jinping-I Dam - 305 m (1,001 ft) in China on Yalong river.
Second Highest is Nurek Dam 300 m (980 ft) Tajikistan on Vakhsh river.

4. Which is the largest Zoo in India ?

Answer: Zoological Gardens, Alipur, Kolkata

5. Which is Longest national highway of India ?

Answer: NH-7 ( Varanasi to Kanyakumari - 2,369 km)

6. Which is smallest planet ?

Answer: Mercury

7. Which is longest tributary river of India ?

Answer: Yamuna