As a general rule, any letters having no vowel or sukoon signs - - - - on them (empty letters) must be treated as silent letters. These silent letters generally occur when long vowel letters (Madd) Alif waw and Ya are involved.
Also letter ‘Lam’ frequently becomes silent where the definite article (al) is prefixed to a word beginning with a letter having its Makharaij ’ points of articulation’ is closed to letter

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