Explanation:

- Option 1: Flute

- The flute is a woodwind instrument used in both Carnatic and Hindustani music traditions.

- It is traditionally associated with artists like N. Ramani and Shashank Subramanyam.

- Option 2: Mridangam

- Correct Answer: Rajna Swaminathan is known for playing the Mridangam, a prominent percussion instrument in Carnatic music.

- The mridangam is essential for maintaining rhythm and is often seen in Carnatic concerts.

- Option 3: Veena

- The veena is a string instrument with significant historical and cultural relevance in Indian classical music.

- Artists like Emani Sankara Sastry and Jayanthi Kumaresh are well-known for playing the veena.

- Option 4: Violin

- The violin is a bowed string instrument adopted into Carnatic music.

- Artists such as Lalgudi Jayaraman and T. N. Krishnan are renowned violinists in this genre.

Rajna Swaminathan is a renowned mridangam player, making Option 2: Mridangam the correct choice.