Interrogatives

Question 1

Welcher (which)

Answer 1

Welcher can be used as a pronoun and a determiner. It declines like ‘dieser’ for both.
Eg welches Bier willst du trinken?

When used as a pronoun in the indefinite sense with sein, ‘welches’ can be used regardless of gender.
Eg welches ist die jüngere Schwester?

Welcher can also be used in exclamations in formal written German but ‘was für‘ is more common in spoken.
Welcher Unterschied!
‘Welch’ is used if ‘ein’ is used
Eg welch ein Unterschied!

Question 2

Was für (what kind of a)

Answer 2

Can be used as a determiner or a pronoun and only the indefinite article declines.
Aus was für einer Familie stammt er?
The case of ein depends on the role of the noun in the sentence - not on ‘für‘

Was is often separated from für
Eg was hast du denn für ein Auto gekauft?

Was für is also used in exclamations (‘what a!’)
Eg Was für eine Chance!

Question 3

Wer/was (who/what)

Answer 3

Wer/was are only used as pronouns. Wer refers to people and was refers to things

Wer/was are usually followed by singular verbs but with sein the appropriate singular/plural is used
Eg wer hat diesen Brief geschrieben
Wer sind diese Leute?

Was is not used with most prepositions and wo is used instead
Eg womit schreibst du?

Wer/was are also used in exclamations
Wer hätte so was erwartet!

Was can be followed by an adjective used as noun with es ending
Was haben Sie Wichtiges besprochen?