The correct answer is option 1, Tamil. Sangam literature refers to the ancient Tamil literature that was written during the Sangam period, which is estimated to have been between 300 BCE and 300 CE. This literature is considered crucial for the reconstruction of the history of South India as it provides valuable insights into various aspects of the region`s society, culture, politics, and economy during that time.

Option 2, Kannada, is incorrect. While Kannada is another Dravidian language spoken in South India, the Sangam literature was not written in Kannada.

Option 3, Telugu, is also incorrect. Telugu is another Dravidian language spoken in South India, but it was not the language used for the Sangam literature.

Option 4, Malayalam, is also incorrect. Malayalam is a Dravidian language spoken in the state of Kerala in South India, but it was not the language used for the Sangam literature.

Therefore, the correct answer is option 1, Tamil, as it was the language in which the Sangam literature was written.