طُوْرِ

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

الطُّوْرُ is the natural state of this definite noun and becomes الطُّوْرِ 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

الطُّوْرِ loses it’s definite article, becoming طُوْرِ due to it being a possessed noun

Mount Sinai, Mount of Olives

To approach

Verse/Below are the 2 verses in the holy Quran, containing the genitive, possessed nounطُوْرِ
Ayat
23-20
95-2and the Mount of Sinaiوَطُوْرِ سِيْنِيْنَ