Explanation:

- Ustad Sultan Khan was a renowned musician known primarily for his exceptional skill with the sarangi.

- The sarangi is a bowed string instrument, prominent in Indian classical music, known for its deep and expressive sound.

- Sultan Khan was celebrated for his ability to bring out the nuanced emotions of the ragas through his sarangi performances.

- Option 1, drums, are percussion instruments and not typically associated with Ustad Sultan Khan.

- Option 3, tabla, refers to a pair of drums used widely in Indian music but was not his primary instrument.

- Option 4, flute, is a woodwind instrument that Ustad Sultan Khan did not specialize in.

Correct Answer: Option 2 - Sarangi