As per the 1991 Census, which one of the following states has a lower population density than the other three?

1. The question asks to identify the state with the lowest population density among Sikkim, Nagaland, Meghalaya, and Manipur, according to the 1991 Census. 2. Population density is calculated as population per unit area (usually per sq. km). 3. According to the 1991 Census data: - Sikkim had a population density significantly lower than the other three states, owing to its mountainous terrain and relatively small population spread over its area. - Nagaland, Meghalaya, and Manipur also have hilly terrain but had higher population densities compared to Sikkim in 1991. 4. Therefore, Sikkim had the lowest population density among the given options.