An apposition is a noun/ noun group, after noun, giving additional information to the first noun and separated with commas.

- 1 The capital of France, Paris, is the largest city of France.

- 2 Paris, the capital of France, is a beautiful city.

In 1 the apposition is Paris, a single noun, in 2 the apposition is the capital of France, a noun group. An appositon is always a noun/noun group, it is not an adjective.

Appositions can be derived from inserted explaning sentences which are shortened as

- 1a its name is Paris

- 2a it is the capital of France

Of course, if you call everything that modifies a noun an adjective you can easily get confused. Adjective is a word class and the term should not be used as a cover name for articles, adjectives, relative clauses and appositions, which all modify a noun.