Which phrase correctly shows the genitive exception with ال?

Cause of Ghayr Munsarif: Sighat Muntaha al-Jumu'

• فِي الْمَسَاجِدَ
• فِي الْمَسَاجِدِ
• فِي الْمَسَاجِدُ
• فِي الْمَسَاجِدٌ