The Sikkimese are known for their mask dance performed by Buddhist monks, known as:

The correct answer is Cham. Cham (also spelt Chaam or Chham) is a masked dance performed by Buddhist monks in the monasteries of Sikkim, as well as in other Buddhist regions of the Himalayas, such as Ladakh, Arunachal Pradesh, Bhutan, Tibet and Nepal. It is a sacred ritual dance and is performed as part of religious festivals.

In the Cham dance, the monks wear elaborate, brightly coloured costumes made of silk brocade, and large painted masks that represent deities, protectors of the faith, animals, demons and other figures from Buddhist mythology. The dances are performed in the courtyard of the monastery, to the music of long horns (dungchen), drums, cymbals and oboes, played by other monks. The movements are slow, dignified and symbolic, and each gesture has a religious meaning. The dances usually depict the victory of good over evil and the triumph of Buddhism over the forces of darkness, and they are believed to bring blessings to the people who watch them and to purify the surroundings. In Sikkim, famous Cham performances are held at the Rumtek, Pemayangtse, Enchey, Tsuklakhang and Phodong monasteries, especially during festivals such as Losar (the Tibetan new year), Losoong (the Sikkimese new year and harvest festival), Pang Lhabsol and the Kagyed dance festival held before Losoong.

About the other options:

• Maruni is a folk dance of the Nepali community of Sikkim, performed especially during the festival of Tihar (Diwali), by dancers in colourful costumes and jewellery.
• Tamang Selo is a lively song and dance form of the Tamang community, performed to the beat of the damphu (a frame drum).
• Chu Faat is a dance of the Lepcha community, performed in honour of Mount Kanchenjunga and its four neighbouring peaks.
• These are all dances of Sikkim, but only Cham is the masked dance of the monasteries.