The correct answer is option 3: Directive Principles of State Policy. The Directive Principles of State Policy are a set of guidelines or principles given in Part IV (Article 36-51) of the Indian Constitution. These principles provide guidance to the government in implementing policies that ensure social and economic justice in the country. They aim to promote the welfare of the people, reduce inequalities, and work towards achieving a just and equitable society.

Option 1, Emergency Provisions, does not ensure social and economic democracy. These provisions are meant to deal with exceptional situations such as war, external aggression, or internal disturbances.

Option 2, Centre-State relations, refers to the distribution of powers between the central government and the state governments. While this is an important feature of the Indian Constitution, it does not directly ensure social and economic democracy.

Therefore, the correct answer is option 3: Directive Principles of State Policy.