فَأَثَرْنَ بِهِۦ نَقْعًا ٤
Sentence structure
فَأَثَرْنَ is a coordinated Form IV feminine-plural perfect; attached نَ is subject. بِهِۦ links to the verb and نَقْعًا is its accusative object.
Ayah summary
Then their swift charge raises a cloud of dust.
فَأَثَرْنَ — then they stir up
Grammar: فَ coordinates; a Form IV feminine-plural perfect, with attached نَ as subject.
بِهِۦ — thereby
Grammar: A preposition with a masculine-singular genitive pronoun, linked to أَثَرْنَ.
نَقْعًۭا — dust
Grammar: An indefinite masculine accusative object of أَثَرْنَ.