In the Preamble to the Indian Constitution, the expression "Sovereign Democratic Republic" figures prominently, indicating that India is an independent nation with a democratic form of government. The expression "Socialist" is also mentioned in the Preamble, indicating that India aspires to establish a socialist society. Similarly, the expression "Secular" is mentioned, indicating that India is a secular country that does not promote any particular religion.

However, the expression "Federal" does not figure in the Preamble to the Indian Constitution. This means that India does not have a federal system of government where power is divided between a central government and individual states or regions. Instead, India has a quasi-federal system where power is concentrated more at the central level.

Therefore, option 4 is the correct answer as it is the only expression that does not appear in the Preamble to the Indian Constitution.