Niyamgiri Hills sit across the Kalahandi and Rayagada districts of Odisha, and the reason they made national headlines was Vedanta Resources' plan to extract bauxite from the range. The area is the homeland of the Dongria Kondh tribe, who regard the hills as sacred ground tied to their deity Niyam Raja and depend on the forest for their livelihood. Acting on a report from a committee led by N. C. Saxena, the Ministry of Environment and Forests turned down clearance for the Vedanta project in August 2010, pointing to breaches of tribal forest rights protections and the serious ecological and cultural damage the mine would cause. The episode became widely cited as a turning point for how tribal rights and environmental law intersect in India.
The other three options belong to different stories altogether. The helicopter crash that killed Andhra Pradesh Chief Minister Y. S. Rajasekhara Reddy happened in September 2009 in the Nallamala forest, a completely different location from Niyamgiri. The Naxalite affected Red corridor is a stretch running through several states, and Niyamgiri is not its headquarters. There was also no such recognition of Niyamgiri as the world's best trekking spot by Conde Nast Traveller. The Vedanta mining controversy, option 1, is the correct reason.