The interrogative pronoun was für ein-

The interrogative pronoun was für ein is used either as an article or as a pronoun in the place of a noun.

Occasionally, was can be separated from für ein.

When functioning as an article, was für ein is inflected as follows.

The pronoun consists of two parts, was für and the indefinite article. The first part remains unchanged and the second part is inflected the same way as the indefinite article.

In the plural and with nouns that indicate material only was für is used.

When functioning as a pronoun was für ein is inflected as follows. The genitive forms are not used.

The pronoun consists of two parts, was für and the indefinite pronoun einer, eine, ein(e)s. The first part remains unchanged, while the second part is inflected like the indefinite pronoun einer, eine, ein(e)s. The plural is formed with welche.

Note

The preposition für in was für ein does not function as a preposition that only governs the accusative; it does not affect the case of ein and welche.

Difference between welcher - was für ein

Welcher is used to ask about one thing from a set of similar things. It indicates choice.

Was für ein is used to ask about the properties, the quality of something.

Exclamations

The pronoun was für ein -like the pronoun welcher-  is also used in exclamations.