Questions & Answers about Какой красивый закат!
Because какой here means what a / what an in an exclamation:
- Какой красивый закат! = What a beautiful sunset!
By contrast, как usually means how:
- Как красиво! = How beautiful!
So Russian uses какой + adjective + noun for this kind of What a ...! exclamation.
It has the same form as the question word какой (which? / what kind of?), but in this sentence it is being used exclamatorily, not as a real question.
Compare:
- Какой это закат? = What kind of sunset is this? → real question
- Какой красивый закат! = What a beautiful sunset! → exclamation
So the form is the same, but the function is different.