Answer : 4. " राजस्थान "
Explanation :

1. Four rivers (Rupangarh, Mentha, Khari, Khandela) fall into Sambhar Lake. Salt is produced on a large scale from this lake.

2. Sambhar Lake: This is a salt water lake located near Jaipur city in Rajasthan state of India. This lake is situated at an altitude of 1,200 feet above sea level.