Learn Icelandic: Borðar þú grænt epli? - Are you eating a green apple?

In Icelandic, adjectives change their endings to match the gender, number, and case of the noun they describe. Because the noun epli is neuter and in the accusative case (since it is the direct object being eaten), the adjective must also be neuter accusative. For strong adjectives, that means adding a -t to the root, making it grænt.

Since epli is the direct object, why doesn't its ending change?

Epli is actually in the accusative case here! It just happens to look exactly the same as it does in the nominative case (the dictionary form). This is a very helpful rule to remember in Icelandic: all neuter words have the exact same form in the nominative and accusative cases.

Why does the sentence start with the verb Borðar?

To ask a yes-or-no question in Icelandic, you simply swap the subject and the verb. Instead of saying Þú borðar (You eat), you put the verb first to make Borðar þú? (Do you eat? or Are you eating?).

Is there a different way to say 'Do you eat a green apple?' instead of 'Are you eating a green apple?'

No, Icelandic uses the exact same verb form for both. Borðar þú can mean either 'Do you eat' as a general habit, or 'Are you eating' right now. You can always tell which one is meant from the context of the conversation.