فَإِذَا جَآءَتِ ٱلصَّآخَّةُ
Sentence structure
إِذَا opens a future non-jussive time-conditioned clause. جَآءَتِ is its verb and ٱلصَّآخَّةُ the subject; the response is supplied by the following context.
Ayah summary
Then the deafening blast of the Day of Resurrection will come.
فَإِذَا — But when
Grammar: فَ is a resumption particle. إِذَا is a time adverb.
جَآءَتِ — comes
Grammar: third-person feminine singular perfect verb; it functions as the condition clause.
ٱلصَّآخَّةُ — the Deafening Blast
Grammar: ٱل is the definite article. nominative noun functioning as the subject.