Ra Rules
Ra Mufakhkham (Heavy)
Heavy when the ra carries fatha, damma, or sukoon following fatha or damma.
The ra is pronounced heavy (with the back of the tongue raised toward the soft palate) in these cases: it carries a fatha (رَ) or damma (رُ); it carries a sukoon and the previous letter has a fatha or damma; it has a sukoon following a kasra arida (a kasra that itself came from the article al-, e.g. الِارْتِيَاب); the previous letter is saakin and itself preceded by a fatha/damma.