Chhattisgarh has the lowest rank in the Human Development Index (HDI) according to the Indian National Human Development Report 2011.

Here are the reasons why Chhattisgarh has the lowest rank:

1. Economic Factors:
- Chhattisgarh is one of the economically backward states in India, with a significant proportion of the population engaged in agriculture and primary sectors. The state faces challenges in industrial development and job creation.
- The per capita income in Chhattisgarh is relatively low compared to other states, indicating lower economic growth and development.

2. Social Factors:
- Chhattisgarh has a relatively high poverty rate, with a significant number of people living below the poverty line. This indicates a lack of access to basic necessities and services.
- The state also faces challenges in education and healthcare. The literacy rate is lower compared to the national average, and there is a lack of quality educational institutions and healthcare facilities in many areas.

3. Infrastructure and Connectivity:
- Chhattisgarh has a relatively underdeveloped infrastructure compared to other states. The road connectivity, particularly in rural areas, is not well-developed, which hampers transportation and access to markets.
- Limited access to electricity and other basic amenities further contributes to the challenges faced by the state in terms of development.

4. Tribal Population:
- Chhattisgarh has a significant tribal population, and tribal communities often face socio-economic marginalization and lack access to basic services, education, and healthcare.
- The development indicators for tribal communities in Chhattisgarh are generally lower compared to other sections of the population, which impacts the overall human development index of the state.

In conclusion, Chhattisgarh has the lowest rank in the Human Development Index due to various socio-economic factors such as low economic growth, high poverty rates, inadequate infrastructure, limited access to education and healthcare, and challenges faced by tribal communities. These factors highlight the need for targeted development interventions and policies to uplift the state and improve the overall human development indicators.