Questions & Answers about Hún er ein af bestu söngkonunum.
Why is it ein instead of the default masculine form einn?
The word for 'one' must agree in gender with the person or thing it refers to. Since hún (she) is female, and the noun she belongs to is söngkona (female singer), we use the feminine nominative form ein. If we were talking about a man, it would be Hann er einn af...
The preposition af means 'of' here. Why does it force the dative case?
The preposition af is a strict grammatical rule-follower: it always forces the noun phrase that follows it into the dative case. In this 'one of' construction, af indicates the larger group you are selecting from, so the entire phrase bestu söngkonunum takes the dative plural.
Why does söngkonunum have such a long ending?
In Icelandic, saying 'one of the...' requires the definite article to be attached to the end of the noun. The base dative plural word is söngkonum (singers). When you add the dative plural definite article suffix -num (the), it stacks together to make söngkonunum (the singers).
If the phrase is dative plural, why is the adjective bestu and not bestum?