The correct answer is Option 2: Malavikagnimitra.

Malavikagnimitra is a Sanskrit play by Kalidasa, an ancient Indian poet and playwright. It is believed to have been written during the 5th century CE. The play revolves around the love story of King Agnimitra, the son of the founder of the Sunga dynasty, and a beautiful maiden named Malavika.

The play portrays the romance between Agnimitra and Malavika, who was a dancer at the court of Vidarbha, a neighboring kingdom. The story goes that Agnimitra falls in love with Malavika after seeing her dance at a royal function. However, he faces several obstacles in his pursuit of her, including competition from another suitor and the disapproval of Malavika`s caretaker.

The play is renowned for its poetic language, intricate plot, and vivid portrayal of characters. It is considered one of Kalidasa`s finest works and a masterpiece of ancient Indian literature.

Option 1, Swapnavasavadatta, is also a Sanskrit play by Bhasa, another ancient Indian playwright. However, it is not about the Sunga dynasty or the love story of its founder`s son.

Option 3, Meghadoota, is a Sanskrit poem by Kalidasa about a Yaksha (a supernatural being) who sends a message to his wife through a cloud. It is a work of lyrical beauty and is celebrated as one of Kalidasa`s greatest achievements, but it is not related to the Sunga dynasty.

Option 4, Ratnavali, is a Sanskrit play by Harsha, an Indian poet and playwright. It tells the story of a princess named Ratnavali and her love interest, the king`s messenger, who disguises himself as a musician to win her heart. While Ratnavali is also a love story, it is not related to the Sunga dynasty or its founder`s son.

In conclusion, the love story of the son of the founder of the Sunga dynasty is depicted in Kalidasa`s play, Malavikagnimitra.