Which food product, nicknamed "The Black Diamond," is primarily produced in Bihar?

Q. Which food product, nicknamed "The Black Diamond," is primarily produced in Bihar?
Answer: Mithila Makhana
Notes: Mithila Makhana, an aquatic fox nut from Bihar’s Mithila region, is called "The Black Diamond." It has a GI tag and key cultural role, with Bihar producing 80% of India's supply. Recognized as a superfood, USA is its top importer; a Makhana Board was announced in 2024 for promotion.