The correct answer is A. Maagh.
Ajitnath Tirthankar was born on the eighth day of the Shukla Paksha of the month of Maagh. He was the 11th Tirthankar of the present Avasarpini. He was born in a royal family in the city of Ayodhya. He renounced his kingdom at the age of 30 and attained enlightenment after 12 years of penance. He preached for 30 years and attained nirvana at the age of 82.
The month of Maagh is the third month of the Hindu calendar. It is a month of great significance for Jains as it is the month in which Ajitnath Tirthankar was born. The eighth day of the Shukla Paksha of the month of Maagh is celebrated as Ajitnath Jayanti. It is a day of great religious significance for Jains and is celebrated with great pomp and show.
The other options are incorrect because Ajitnath Tirthankar was not born on the eighth day of the Shukla Paksha of the months of Chaitra, Ashwin, or Jyestha.