Answer : 1. "Union of States "
Explanation :

(a) Union of States: This means that India is a federation comprising states and union territories. It emphasizes the unity of the country while recognizing the diversity and autonomy of its states.

(b) Federal State with Unitary Features: India operates as a federal state where power is divided between the central government and individual states. However, there are certain unitary features, such as a strong central authority in matters like defense and national security.

(c) Federal State with Federal Features: This is not a term used to describe the Indian political system. India is often termed as a federal state with unitary features.

(d) Federal State: This term generally implies a political entity where power is shared between a central government and regional entities. India is indeed a federal state where states have their own governments and certain powers, alongside a strong central government.