The correct answer is (b), Vaishali.
The first Jain council was held in Vaishali in 543 BCE, 100 years after the death of Mahavira. It was convened by the Ganadharas, the chief disciples of Mahavira, to discuss and codify the teachings of the Tirthankara. The council was attended by over 1,200 monks and nuns.
The council was a major event in the history of Jainism. It helped to preserve the teachings of Mahavira and to establish the Jain religion as a major force in Indian society.
The other options are incorrect.
(a) Patliputra was the capital of the Mauryan Empire. It is not known if the first Jain council was held there.
(c) Mathura was an important city in ancient India. It is not known if the first Jain council was held there.
(d) Ujjain was an important city in ancient India. It is not known if the first Jain council was held there.