The Namgyal Dynasty, which ruled Sikkim for centuries, was established by:

The correct answer is: a) Phuntsog Namgyal.

Phuntsog Namgyal was a Tibetan Buddhist lama who founded the Namgyal dynasty in Sikkim in 1642. He was born in Kham, Tibet, in 1594. In 1616, he was invited to Sikkim by the local ruler, Tensung Namgyal, to help him repel an invasion from Bhutan. Phuntsog Namgyal was successful in defeating the Bhutanese, and he was subsequently installed as the ruler of Sikkim. He ruled Sikkim until his death in 1672.

Phuntsog Namgyal was a wise and just ruler. He established a strong central government and promoted religious tolerance. He also built many temples and monasteries in Sikkim. Phuntsog Namgyal is considered to be the founder of modern Sikkim.

The other options are incorrect because:

• Kheyi Bumsa was a Tibetan Buddhist lama who lived in the 16th century. He is not known to have had any connection with Sikkim.
• Tensung Namgyal was the ruler of Sikkim from 1616 to 1642. He invited Phuntsog Namgyal to Sikkim to help him repel an invasion from Bhutan.
• Chakdor Namgyal was the son of Phuntsog Namgyal. He ruled Sikkim from 1672 to 1675.