Explanation:

Longest-serving Chief Minister of India: Pawan Kumar Chamling is one of the longest-serving chief ministers of India along with Jyoti Basu. Pawan Kumar Chamling was the Chief Minister of Sikkim from 12 December 1994 and has been serving since then.

Pawan Kumar Chamling has served for five successive terms since 1994 and has served as the Longest serving Chief Minister of Sikkim for 24 years, 205 days. Jyoti Basu served as the Chief Minister of West Bengal from 1977 to 2000. He has served as the Chief Minister of West Bengal for 23 years, and 137 days.