No rule for this one
No ending or word group predicts the article of Antrag. Learn it as a pair and say it out loud: der Antrag.
der Antrag
It's der Antrag. Antrag is masculine, plural die Anträge.
Ich stelle einen Antrag.
I submit an application.
No ending or word group predicts the article of Antrag. Learn it as a pair and say it out loud: der Antrag.