In which one of the following districts, have large reserves of diamond-bearing kimberlite been discovered in the recent past?

The correct answer is Raipur (option 2). Geological surveys in the 1990s and subsequent investigations by the Geological Survey of India and state directorates led to discovery of diamond-bearing kimberlite pipes (Behradih, Payalikhand and others) that together form the Mainpur Kimberlite Field in southeastern Raipur district, Chhattisgarh; several of these diatreme‑facies pipes have been confirmed as diamond‑bearing within a roughly 16×5 km zone. While Panna in Madhya Pradesh has historically been India’s principal diamond‑producing district, the more recent identification and mapping of kimberlitic pipes near Raipur mark a significant new reserve of diamond‑bearing kimberlite in central India and warrant further resource evaluation [1].

Sources

1. [1] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 7: Resources > Natural Resources of India > p. 29