فَأَكْثَرُوا۟ فِيهَا ٱلْفَسَادَ
Sentence structure
فَأَكْثَرُوا۟ is a masculine-plural Form IV perfect; attached و is the subject. ٱلْفَسَادَ is its accusative object, while فِيهَا is linked to the verb.
Ayah summary
And they spread great corruption within them.
فَأَكْثَرُوا۟ — And (made) much
Grammar: فَ coordinates/results; أَكْثَرُوا۟ is a Form IV masculine-plural perfect and attached و its subject.
فِيهَا — therein
Grammar: فِى is a preposition and attached هَا a feminine-singular pronoun in the genitive position. This phrase is linked to «أَكْثَرُوا۟».
ٱلْفَسَادَ — corruption
Grammar: ٱل defines the masculine accusative object فَسَادَ.