Consider how the parts relate to the whole.
In a federal state, the constituent states belong to a shared constitutional order. The Länder have their own tasks but remain parts of the Federal Republic. This is more than an agreement among independent neighbouring countries.
The contrasting term unitary state emphasises one central state authority. Regional administrations may exist there too; their mere presence does not make a federal state. What matters in Germany is the Länder’s own constitutional responsibilities.
The other three answers
Word order alone is not an explanation.
confederation of states.
Association of states is not Article 20’s description of Germany. The question asks for the state as a whole with its Länder.
confederation.
A confederation links states that remain fundamentally independent. Germany is a federal state with constituent states.
centralized state.
Unitary state does not describe the constitutional division between federation and Länder.
Federal does not mean identical arrangements everywhere.
The allocation of responsibilities can differ between federal states. This question concerns Germany and the description in its Basic Law.
Central and decentralised elements also work together within Germany. Differences between Länder can coexist with shared federal rules.
Article 20 · Basic Law ↗Federal state: one state, several Länder.
Think of the shared whole and the distinct tasks of its parts.
Three words for this question
- der Gliedstaatconstituent state
- A state forming part of a federal state.
- der Staatenbundconfederation
- An association of fundamentally independent states.
- der Zentralstaatunitary state
- A state whose governmental organisation is centred in one authority.