The Chogyal (Dharma King) was both the temporal and spiritual leader of Sikkim. His coronation ceremony took place at:

The correct answer is: c) Rumtek Monastery.

The Chogyal (Dharma King) was both the temporal and spiritual leader of Sikkim. His coronation ceremony took place at Rumtek Monastery, which is located in the East Sikkim district of India. The monastery is the seat of the Karmapa, the head of the Kagyu school of Tibetan Buddhism. It was founded in 1692 by the 8th Karmapa, Dudjom Rinpoche. The monastery was rebuilt in the 19th century by the 12th Karmapa, Tai Situpa. It is one of the largest and most important monasteries in Sikkim.

The other options are incorrect because:

• Pemayangtse Monastery is a Buddhist monastery located in the West Sikkim district of India. It was founded in 1642 by the first Chogyal of Sikkim, Phuntsog Namgyal. The monastery is the seat of the Nyingma school of Tibetan Buddhism.
• Norbugang Chorten is a Buddhist chorten located in the East Sikkim district of India. It was built in the 17th century by the 5th Chogyal of Sikkim, Thutob Namgyal. The chorten is a sacred site for Buddhists and is believed to be a repository of Buddhist relics.
• Khecheopalri Lake is a lake located in the East Sikkim district of India. It is a sacred lake for Buddhists and Hindus. The lake is believed to be the home of the goddess Tara.