Two feminine plural forms remain unchanged under لَنْ in this paradigm:
يَفْعُلْنَ
تَفْعُلْنَ
Their final Noon is not the Noon-e-I'raabi of the seven forms. It is part of the feminine-plural subject pronoun and remains fixed here.
So:
لَنْ يَفْعُلْنَ
لَنْ تَفْعُلْنَ
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Group 3: Two Feminine Plural Forms Stay Unchanged
Rule of Emphatic Negation in Future with "Lan" (لَنْ)
Two feminine plural forms remain unchanged under لَنْ in this paradigm:
يَفْعُلْنَ
تَفْعُلْنَ
Their final Noon is not the Noon-e-I'raabi of the seven forms. It is part of the feminine-plural subject pronoun and remains fixed here.
So:
لَنْ يَفْعُلْنَ
لَنْ تَفْعُلْنَ