Answer : 3. "Pataliputra "
Explanation :

The first Jain council, known as the First Jain Council of Pataliputra, was held in Pataliputra. This council is believed to have taken place around 300 BCE, shortly after the death of Lord Mahavira, the 24th Tirthankara of Jainism. The purpose of the council was to compile and codify the teachings of Mahavira, ensuring their preservation and transmission. Pataliputra, an ancient city in present-day Bihar, India, was a significant center for intellectual and religious activities during that period.