1. Which is the longest wall in world ?

Answer: Great wall of China

2. Longest rail tunnel in the world ?

Answer: Seikan Tunnel (Japan - 53.9 Km)

3. Which is the Largest lake of the world ?

Answer: Caspian Sea (371,000 sq km)

4. 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.

5. Which is the longest day in the year ?

Answer: June 21

6. Which is largest Delta of India ?

Answer: Sundarban (W. Bengal)

7. Which is the largest Mosque in India ?

Answer: Jama Masjid (Delhi)