Explanation:

- Sikkim: This state had the least population among the options provided as per the 2011 Census. It is known for its small geographical size and mountainous terrain.

- Bihar: One of the most populous states in India. It has a large population density and significant urban and rural populations.

- Kerala: Known for its high literacy rate and human development index. It is more populous than Sikkim.

- Chhattisgarh: Although less populated than Bihar and Kerala, it still has a much larger population compared to Sikkim.

Correct Answer: Option 1 - Sikkim