نَارِ

A word in the Arabic language will either be 1) a verb or 2) a noun or 3) a particle – نَارِ is a noun

A noun may either be 1) Definite or indefinite 2) Masculine or feminine 3) Singular, dual or plural 4) Nominative, accusative or genitive

النَّارُ is the natural state of this definite noun and it becomes النَّارِ due to: 1) a preposition that precedes it or 2) a possessed noun that precedes it or 3) it’s a noun of dependent declension a) نَعْتٌ / صِفَطٌ adjectives b) التَّوْكِيْدُ emphatic c) المَعْطُوْفٌ conjunction d) البَدَلُ synonym

النَّارِ loses it’s definite article, becoming نَارِ due to it being a possessed noun

Fire, Burning flame, Heat, War

To emit fire or light, shine, sparkle, irritate, vex or provoke war, create heat

Surah/Below are the 5 verses in the holy Quran containing the genitive, possessed nounنَارِ
Verse
On the day it will be heated in the fire of hell and will be branded with itيَوْمَ يُحْمَى عَلَيْهَا فِيْ نَارِ جَهَنَّمَ فَتُقْوَى بِهَا
their foreheads and their flanks and their backsجِبَاهُهُمْ وَجُنُوْبُهُمْ وَظُهُوْرُهُمْ
9-35“This is what you hoarded for yourselves so taste what you used to hoard”هَذَا مَا كَنَزْتُمْ لِأَنْفُسِكُمْ فَذًُوْقُوا مَا كُنْتُمْ تَكْنِزُوْنَ
then is one who founded his building on fear of Allah (SWT) and His pleasureأَفَمَنْ أَسَّسَ بُنْيَانَهُ عَلَى تَقْوَى مِنَ اللهِ وَرِضْوَانٍ
better or who founded his building on the edge of a cliff about to collapse so, it collapsed with him (in it)خَيْرٌ أَم مَّنْ أَسَّسَ بُنْيَانَهُ عَلَى شَفَا جُرُفٍ هَارٍ فَانْهَارَ بِهِ
9-109in the fire of Hell and Allah (SWT) does not guide the wrongdoing peopleفِيْ نَارِ جَهَنَّمَ وَاللهُ لَا يَهْدِي القَوْمَ الظَّالِمِيْنَ
15-27
52-13
Truly those who disbelieve from the people of the book and the polytheists will be in the fire of hellإِنَّ الَّذِيْنَ كَفَرُوْا مِنْ أَهْلِ الْكِتَابِ وَالْمُشْرِكِيْنَ فِي نَارِ جَهَنَّمَ
98-6abiding therein forever, those are the worst of creaturesخَالِدِيْنَ فِيهَآ أُوْلَآئِكَ هُمْ شَرُّ البَرِيَّةِ