1. Longest rail tunnel in the world ?

Answer: Seikan Tunnel (Japan - 53.9 Km)

2. 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.

3. Which is the highest Plateau ?

Answer: Pamir, Tibet

4. Which is largest Delta of India ?

Answer: Sundarban (W. Bengal)

5. What is the name of brightest star ?

Answer: Sirius

6. Which is longest river in world ?

Answer: Nile, Africa

7. Which is the longest day in the year ?

Answer: June 21