The correct answer is option 3: National Development Council. Chief Ministers of states are members of the National Development Council. The National Development Council is a body that consists of the Prime Minister, Union Ministers, and the Chief Ministers of states and Union territories. It acts as a platform for the Central and state governments to discuss and deliberate on matters related to national development and policy planning. The council plays a crucial role in coordinating and formulating plans and policies for economic and social development in India. It facilitates cooperation and collaboration between the Central and state governments to ensure balanced and inclusive development across the nation. The NITI Commission (Aayog) mentioned in option 1 is incorrect, as Chief Ministers are not members of it.