Step 1: Understanding the Concept:
Article 1 of the Constitution of India defines the name and the nature of the Indian polity. It is the very first article and sets the foundational understanding of the country's structure.
Step 2: Detailed Explanation:
Article 1(1) of the Constitution reads: "India, that is Bharat, shall be a Union of States."
The Constituent Assembly deliberately chose the term "Union of States" over "Federation of States". Dr. B.R. Ambedkar explained that the term "Union" was used to signify two important things:
\begin{enumerate}
\item The Indian federation is not the result of an agreement among the states to join a federation.
\item The states have no right to secede from the federation. The Union is indestructible.
\end{enumerate}
While India has a federal structure (with power divided between the Centre and States), the term used in the Constitution is 'Union of States'. The terms 'Democratic republic' describe the nature of the government as laid out in the Preamble, and 'Quasi-federal' is a description used by constitutional scholars to explain India's structure (federal in form but unitary in spirit), but it is not the term used in Article 1.
Step 3: Final Answer:
Article 1 of the Constitution explicitly declares that India shall be a "Union of states".