Is Xylofon der, die or das?

The correct German article for Xylofon is das. The noun Xylofon is Neuter. So you always say: das Xylofon. Learn the article together with the noun — German nouns don't follow predictable gender rules most of the time.

The plural of Xylofon is: die Xylofone. In the plural, every German noun takes the article "die". So: die Xylofone. Example: ein Xylofon → zwei Xylofone.

Correct: die Xylofone. The form "die Xylofons" is wrong. The plural of das Xylofon is die Xylofone. In the nominative plural, you always use the article "die".

das Xylofon follows the four German cases. Nominative: das Xylofon, Accusative: das Xylofon, Dative: dem Xylofon, Genitive: des Xylofons. In plural: die Xylofone / den Xylofonen. Learn these forms together with the noun.

The genitive singular of das Xylofon is: des Xylofons. The genitive plural is der Xylofone. German uses the genitive to express possession or belonging. Example: die Farbe des Xylofons.

The dative plural of Xylofon is: den Xylofonen. In German, dative plural nouns usually end in "-n". So you say: "mit den Xylofonen". Use this case after prepositions like mit, von, bei, zu.

Xylofon is a noun and must be capitalized in German. You'll find example sentences above for each case. The article das stays the same in nominative singular but changes in other cases. Practice declension in your own sentences.

Yes, Xylofon is a noun (also called a substantive). German nouns are always capitalized. The article for Xylofon is das. Every German noun has a fixed article you must memorize.