If a final ra becomes still at a pause, the immediately preceding consonant is also still, and the meaningful earlier vowel is kasrah, the ra is generally light.
«الذِّكْرِ» when paused upon: ra becomes still, kaf before it is still, and dhal before kaf has kasrah; the final ra is light.
First establish how the word is being read at the pause, then inspect the preceding sounds. In connected recitation the final ra may itself have kasrah and therefore be light for a different, simpler reason.
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Refining Qualities and the Detailed Rules of Lam and Ra
If a final ra becomes still at a pause, the immediately preceding consonant is also still, and the meaningful earlier vowel is kasrah, the ra is generally light.
«الذِّكْرِ» when paused upon: ra becomes still, kaf before it is still, and dhal before kaf has kasrah; the final ra is light.
First establish how the word is being read at the pause, then inspect the preceding sounds. In connected recitation the final ra may itself have kasrah and therefore be light for a different, simpler reason.